Of course there are always two folders “Program Files” (64 bit apps) and “Program Files (x86)” (which is for ancient 32 bit versions of apps)
In fact, I observe that Unity (this is Unity4 … is 5 the same??) installs a folder in both of these.
Can I simply erase from existence the stupid “Program Files (x86)/Unity” folder?
Rather, should I use the Uninstall.exe which is INSIDE the “Program Files (x86)/Unity” folder … or in fact, would that delete both/all my unity builds?!
If having two folders bother you, and you don’t mind reinstall Unity, you can specify Unity to install to a chosen directory. All its stuff will be placed there and no Program Files (x86) will be used. As I’m working on a virtual machine, I install all my programs inside D:\Programs\ so I don’t have to reinstall them whenever I have to reinstall the system (since I am a virus paranoiac, it happens often). Programs using registry keys will most of the time update themselves to the new database.
If anyone wonder if this is okay for Windows 7 too, Windows 8 treats x86/x64 folders the same so you can.
To strictly answer your initial question “can I delete them”, it is not recommanded since - as you stated - you can find inside the uninstaller. Deleting it will give you troubles to uninstall Unity. The fact is Unity 4 only have one installer for 32/64 bit systems. It is an external program with its own rules. Since Unity 4 is a x86 program, it will put the uninstaller inside this folder (until you tell it not to by changing the install folder). What is safe is to move the uninstaller, you can move it to the x64 folder with no issues. You can try to move the other files too. My guess is that the only trouble you’ll get is that the uninstaller won’t be able to remove the moved files when you’ll have to uninstall, but this won’t pop any error. You will need to remove the file manually.
Using the uninstaller will only delete files relative to its installation, so if you use 4.3 uninstaller, it won’t delete 4.6 files (except if you overwritten 4.3 files, but in this case 4.3 uninstaller should have been overwritten too). But it will delete files in both Program Files & Program Files (x86). So, don’t use it untill you want to remove Unity.
Yet, I am using a personnal license and I can’t use all the features (plus, I now use version 5), so if you are on a Pro license, you should do your own test cases: move the folder and try to use Unity. If you got any error message, it needs the files.