Anything you can delete in any temp folder is safe to delete.
Any file in use will have open handles & will therefore me locked, preventing deletion or renaming.
The easiest way to delete your temporary files is as geno suggested.
There is a temporary folder for every user on the PC, plus the windows temporary folder, plus an internet explorer temporary folder & also an undelete folder.
The cleanup wizard will get them all in one go & also offer compression for any files which are rarely used.