How do I open a file from Wc3 on gimp?

I just dled theGimp and I need to know how to open a unit from wc3 to edit it :?

and before anyone posts it, I know it's a stupid question, probably with an easy answer, but I just started out and need help.

All serious posts will be greatly appreciated.

i tried entering the file name but GIMP says .mdl is not a recognized file type, and i can't access .blp either for some reason.