At this point I would safely say that 98% of the people who have used Cakewalk for a long time and have been through upgrades going back to versions like Sonar 6 and 8.5, the X1 fiasco then Splat--- have by now  "Upgraded" to the Bandlab version. And 98% of those folks did this without issue fuss or worrying about the world coming to an end. 
Nothing will happen to SPlat or to 8.5 for that matter. They just stay put as they always were. 
Cakewalk has always come out with new versions about once a year. Those have always been NEW version that coexist with the older versions.  There is a huge difference between an Upgrade and an Update with all software. Updates are the ones that overwrite the original. In most cases this can be rolled back.  
 
Upgrades usually cost money, Updates are usually free. 
This is an Upgrade that just happens to be free. 
And it is by no means the Home Studio version, That comment was sort of out of turn.
It is fully the Platinum version feature wise. The only relationship to Home Studio is that it comes with a stripped down VST collection. This is because they cannot give away for free things like Melodyn and Addictive drums.  

Toddskins
 
You must know about Image backups, right?  Norton Ghost v.15 for Windows 7, or Acronis True Image and others for Windows 10.

So simply make an image backup of your C-drive before the new install of CbB, and stop worrying.  Restore the image if you have bad dreams.

It appears that it is you that doesn't understand image backups.  On the 1TB drive holding Cakewalk Sonar are all my wave files and additional sound programs coming close to 600Gb.  Creating an image backup is just not practical.
 
I have to say that I am stunned.  I have outlined a simple problem and no one here is able to help me even though it is information that many here have.  I need to update Sonar Platinum.  How do I do so and still keep the features I have?  The advice I have been given is ambiguous - overwrite, separate installation, or separate disk?  Is this lack of clarity due to confusing or unexplained prompts during the upgrade process?
 
Where is the documentation for the upgrade process explaining the prompts and choices?   

Johnny V of Cactus Music,
 
Thank you.  I did not see this when I posted above.  Your post does indeed clarify the situation.  Thank you.

djwolf

Toddskins
 
You must know about Image backups, right?  Norton Ghost v.15 for Windows 7, or Acronis True Image and others for Windows 10.

So simply make an image backup of your C-drive before the new install of CbB, and stop worrying.  Restore the image if you have bad dreams.

It appears that it is you that doesn't understand image backups.  On the 1TB drive holding Cakewalk Sonar are all my wave files and additional sound programs coming close to 600Gb.  Creating an image backup is just not practical.
 
I have to say that I am stunned.  I have outlined a simple problem and no one here is able to help me even though it is information that many here have.  I need to update Sonar Platinum.  How do I do so and still keep the features I have?  The advice I have been given is ambiguous - overwrite, separate installation, or separate disk?  Is this lack of clarity due to confusing or unexplained prompts during the upgrade process?
 
Where is the documentation for the upgrade process explaining the prompts and choices?   

I haven't read the entire thread, but to answer your questions, just download & install CbB. If you don't have an account with Bandlab, open one but use exactly the same email & password as you do for here.
The installation will install in parallel with any existing installation and will not interfere with it in any way. You are free to use any version at any time (barring backwards compatibility of certain features such as Patch Point & Aux Tracks- but you do mention you're running Platinum so even this isn't an issue).
Once CbB is installed, go into Platinum and make a note of your vst Scan paths.
Then go into CbB and ensure these paths are replicated in the Plugin Manager
 
Looking to the future, you might want to install a separate hard drive or 2 and split the contents of your current drive so that one contains the OS & programs, another for your Cakewalk Projects & Wave files, and a third for your sample libraries
 

djwolf

Toddskins
 
You must know about Image backups, right?  Norton Ghost v.15 for Windows 7, or Acronis True Image and others for Windows 10.

So simply make an image backup of your C-drive before the new install of CbB, and stop worrying.  Restore the image if you have bad dreams.

It appears that it is you that doesn't understand image backups.  On the 1TB drive holding Cakewalk Sonar are all my wave files and additional sound programs coming close to 600Gb.  Creating an image backup is just not practical.
 

>Creating an image backup is just not practical.
Not trying to be rude or snide but frankly it is or should be to you, if you were serious about not losing your data.
My DAW laptop has 2 internal 1 TB drives and a external 4TB HD and somehow I manage.
If your serious about stuff you find a way to back it up, regularly.
Be it an 'act of god' (power transformer shorting out, a lightening strike, a car hitting a power pole, etc.), act of CAT (STAY OFF MY DESK VARMIT!) or just old plain old age/wear & tear - all electronic equipment will fail sooner or later, often without warning.
The question is when is does are you screwed or are you prepared?