Deleting files on a PC is normally very easy. But sometimes, just occasionally, Windows will tell you that it can't help because the file is "in use". And that can quickly become very frustrating, especially if you can't see why the file is open, or it's something you really need to delete (a malware component, say).
To resolve this you should try closing all running applications, rebooting, perhaps try to delete the file from Safe Mode. But if this doesn't work then you could always turn to ForceDel, a command line tool which can forcibly delete files, even if they're open in another application.
Don't be put off by its command line nature - ForceDel is extremely simple to use. There are a few command line switches (run ForceDel on its own to see them), but essentially all you have to do is give the program the name of the file you'd like to delete - ForceDel "c:\users\MyName\Desktop\Annoying.zip" - and it'll try to close any open handles, before eliminating the file for you.
And if you want to keep things really simple, there's not really any need to use the command line at all. Just drag and drop the file you want to delete onto ForceDel, and the program will remove it right away.
Please note, you need to use programs like this with extreme care. If Windows or an application thinks it has a file open, but in fact you've just deleted it, then there's no way to tell exactly what might happen next: crashes, lockups, maybe nothing at all. So you should use ForceDel only when absolutely necessary. Save any work before you do so, and restart your system as soon as possible afterwards.