Ok, well if you're using Windows right click on one of your picture files, go down to open with...and that should give you a drop-down menu of programs associated with that file type.
If you have Windows you at least have Paint. If a better program doesn't rear it's head open them up in Paint and resize them. Only I don't think paint has a resize command, it's called skew, or something like that. Just skew both axes the same % and it's effectively resized.