How to delete thumbnail cache

Hello. I have Windows 7 and I have upgraded to the pay version of CCleaner. When I run the program it seems that there are always some items left in the thumbnail cache under app data/local/microsoft/windows/explorer. I have run the program several times and it seems it never quite empties it. How do I fix this? Please be aware I am a beginner to this. Thank you in advance for any help.

Can you have Windows delete all of them in OS(C:)\ Properties\ Disk Cleanup\ Thumbnails ?

Tried that. It did not do anything.

They are necessary if Windows won't delete them. I have many. Don't mess with them.