try googling “unlocker” it can be used to delete files on reboot. or, you can download a Linux live cd (try googling Ubuntu live cd) and then burning it and booting up from it. It can access the file and delete it that way.
If you need any help with these two options, or for some reason need a third option, don’t hesitate to ask!
P.S. If the file is really small or something, and you don’t really care THAT much, then I would recommend just leaving it.