Actually it's not a solution for everyone, for many the only solution is to reboot or sign out and back in.
The problem is the file stays in use or was already in use before you even touched it and at that point it can not be moved, removed or deleted.
I have been able to delete the contents of the folder and then delete the folder but sometimes the contents are in use and therefore cannot be deleted.
Preview has never been enabled on my PC 8.1, however there has been the occasion that by leaving the file and folder alone for a period of time I can then delete it.
Indexing could be the problem but I have never turned it off to validate this.
I was hoping this would be corrected in W10 but I uninstalled W10 30 minutes after I installed it because it sucked for many reasons including MS control of updating.