SHOULD I CLEAN ALL MY CS5 FILES FROM COMPUTER?

Hi @Bill in Norcal,

Old Creative Suite and new CC apps are installed in separate folders. They don't share anything. 

You may safely remove the old software if you no longer need it.  Use the Adobe Cleaner Tool below.

https://helpx.adobe.com/creative-cloud/kb/cc-cleaner-tool-installation-problems.html

Hi. Sometimes there are templates and swatches and brushes you may want to save and employ in the new version (LOTS of the panels have changed, and the old stuff had broader default selections in some cases). But, the new PS doesn't USE them (lots of people never had those versions and the software works... self-contained), unless you employ them. Any leftovers from the old CS aren't needed - so if you want to clear them out, I'd say go for it.