How to identify redundant windows files

I was seeing my system slowly fill up the drives but I was not installing new files. While looking today I find there's a 16 gig files called windows.old and a couple other $windows folders. I've also got 20 C++ libraries on my system in 32 and 64 bit formats.
 
It seems most of this stuff is just taking up space but I don't know if I can delete any of it.
 
I need a computer wiz to help me sort out the junk, any ideas?

I suggest getting CCleaner... works great. Also, I deleted windows.old because I don't plan on rolling back to Win8.1

I avoid the "duplicate file finder" programs.  A same file may be in two different locations and the applications that use that file may only look at specific locations.  If the duplicate file has been removed from one location, and its the one that a specific application uses it will error since it won't look at another location that has the file.

Def. clean up (AKA delete) any files under users\<you|anybody>\AppData\Local\Temp, often a few GBs rack up there.  Often one or two files will be in-use/locked, but you can blow away the rest.
 
Also, temporary internet files can build up over time, I recently removed a bunch of them dated 2010-2013 (?!) which amounted to another couple of GBs.  c:\users\<you|Default|anybody>\AppData\Local\Microsoft\Windows for the IE temporary internet files folder, not sure about Mozilla/Chrome/Opera etc. (simple enough to search).
 
Regarding the Windows.old folder, I believe that Windows cleans this up after a month of so of it hanging around, it's the OS which you upgraded from.  You could always back it up in case you want to go back to the previous version of Windows.
 
Pretty much all installers leave tons of guff hanging around in the system registry, you can free up some space by running a decent registry cleaner against it.  I think CCleaner is about £20.
 
Another thing worth checking is the location/size of the swap and hibernation files (pagefile.sys, hiberfil.sys).  I believe that you have some control over the size & location of the swapfile and possibly the location of the hibernation file.  This can also help to free up q. a bit of space.
 
Also, check your downloads folder, this can often get rather large.
 
HTH :-)
 
p.s. I only have 17 C++ redistributable packages installed, but I do have 34 separate M$ SQL Server packages installed - go me!  I guess they'll come in handy if I ever actually use SQL Server..?!

in ccleaner there is also a dupe file finder,  under tools menu..  which I've found useful
 
the other thing , look for "tree size free" by jam software, it'll show you bloated area's of ya drives
 
the most bizarre one I had years ago, on my sisters machine.. was a few 4mb photo's was reporting as 4gb.. so loading em up and re-saving em magically made em shrink instantly :)
 
have a look for things like "pdf" as you may find you have some foreign language ones also
 

D­u­p­l­i­c­a­t­e­F­i­l­e­s­D­e­l­e­t­e­r is a simple, but effective tool to locate duplicate files in one or more selected search paths. It scans the files and compares them based on Byte for Byte Comparison, which ensures 100% accuracy. You can then choose to delete the selected duplicate or original files. The program is multi-threaded and performs scans quickly.

From a "duplicate" standpoint, duplicates on a single drive are highly unlikely and are normally created by a user copying files to other locations. Typically backup media will contain duplicates over anything else, especially if the user changed (main) folder structure or file locations between backups.
 
From a space perspective, a simple check for a drive is using Windows Explorer, selecting the drive, and click the search box in the upper right. Selecting "Size" and going through "Gigantic (>128MB)" and a second pass on "Huge (16-128MB)" will often give insight on offenders. Temporary directories for audio/video programs are a big one to watch because of the size of these data files, but most also allow assignment of this directory in the stand-alone version of the software (e.g., Melodyne). Download folders, and temporary directories are another (also covered above in BobF's post).

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