What should I do if I can't delete files from the printer spooler folder?

If you can't delete files, ensure the 'Print Spooler' service is stopped. If that doesn't work, take ownership of the folder: right-click the 'PRINTERS' folder, select 'Properties', go to the 'Security' tab, click 'Advanced', change the owner to your user account, and grant yourself full control. Then try deleting the files again.