As a rule your temp folder should empty when you close programs that use it.
Or the file space in the temp folder is overwritten as it's limit is reached.
You can manually delete all the files in your temp folder anytime you like, if files are in use they won't be able to be deleted. Close the program and these files can then be deleted.
You can access your temp file by going to Windows Start and typing %TEMP% the folder will show up and you click on the folder to open. Ctrl+A to select all. Ctrl+D to delete.