How to I change file type?

Does anyone know how to change file type? Looking at an icon of a zip file, when I go to properties is tells me "004 File (.004)" is the file type. WinRar, 7zip, and WinZip can't open the file as an archive.

Thanks.

A file with those numbers at the end is meant to be a part of a set of files. 001, 002 and so on. The key: these files are not meant to execute on their own, instead a .7z or whatever is supposed to be the starting file. They are split for convenience in download or filesystem limitations ie, the whole thing is huge. If you don't have this file or the rest of the set (wherever you got it should have everything you need, in its own space) then the .004 is just a useless fragment. If you don't have the rest then you need to look for or redownload the full set of whatever you're looking at.