so can you install this new version and have both versions on your PC at the same time?

Do you need to uninstall the old one first?

Yes the "solution" using junctions is easy but is still a workaround at best for a SW installer that puts stuff all over boot drive.    SW files and SW programs can be, and are, installed anywhere - the PROGRAM should keep track of locations - like a significant portion of other SW does. 
 
But back to junctions:  (and note, this is the lazy and sloppy way to write new install code)  Yes, its so easy to use junctions that even a first year apprentice coder at CW/Gibson/BandLab could modify the installer to ASK the USER what path to use to install everything then installer application can be modified to 1) create said junction using that user supplied path, then 2) simply install as before using the rest of the "old" installer code, all future updates will take care of themselves.  The end result is the USER doesn't have to mess with it.
 
Of course a more professional way is to actually modify the installer(s) to ask user where to put stuff and actually create those paths and update program configurations and registry information to look at those paths for "stuff" and keep track of those paths for the USER. 
 
CW installs, and this goes back before Band Lab, has been a mess since approximately Sonar 5 or 6 (I'm old I forget its whenever Vista was the OS).  And its over this very issue, coupled with some snarky and dismissive replies by actual CW staff members, not simple sonar forum users,  that I left Sonar a full year before Gibson dropped it.   And for the record,  I was no "johnny come lately"  to Sonar and I'd been using Cakewalk, and loyally, through EVERY version up to SPLAT Lifetime, since Cakewalk for DOS version 2. 
 
I only monitor Sonar now to see what happens and see what Band Lab can do with it, but unlikely I'll move back, even for free.  As a matter of fact I'm really standoffish now due to the BL assistant. I installed and about five minutes later uninstalled the Band Lab Assistant because it embedded itself in the registry as run at start up entry (HKEY current user .... \run registry)  bypassing ability for user to easily  enable/disable via task manger Start Up) 
 
I do wish all new and current users of the new Band Lab free Sonar the best of luck,  I truly hope it helps them produce good music easily.

Yeah, it is in the registry. AFAIK from later reports, CbC uses the same setting HKEY_LOCAL_MACHINE\SOFTWARE\Cakewalk Music Software\ContentDir so if it has been altered either using the Command Center or manually, CbC will honor it. Rather than take chances, at the time I recommended a directory junction. I still prefer the method.

Seriously bandlab thought thousands of users should rather go though a workaround rather than having someone program the installation file like how all apps do?