Some applications lock their opened files which means you cannot simply rename or delete them. In most cases, this makes sense and it is not advisable to circumvent it. However, there are situations where you might want to unlock a file, like when a program crashed and you want to delete its locked files. Usually you have to reboot for this, but you can do this faster with Unlocker, a free Windows tool.
Unlocker can automatically start the moment you try to rename or delete a locked file. You, then, have the option to unlock the file or kill the process that has locked the file. Be sure that you know what you are doing. Some programs don’t forgive such rude behavior and you might lose data. If you already know that a file you want to change is locked, you can unlock it by right-clicking on it in the Windows Explorer.