Can't delete a file I created in Windows

I'm downloading a file into a MemoryBlock and then creating a temp file and writing the block to it:

file = file.createTempFile("tmpFile");
FileOutputStream* os = file.createOutputStream();

if (os->write(mb.getData(), mb.getSize()))

I then copy this file to some other location, and try to delete it using file.delete();

It does not work. When trying to manually delete the file using the Windows Explorer, it says that my application is locking it.

How can I release the file/handle and just delete it?

Maybe try not leaking your FileOutputStream object!