John in NM
I use Gimp for resizing, you can simply scale the image and save it as a new name, then there's a little preview checkbox on the save screen. Check that and it will tell you how big the file will be and you can turn the image quality up or down to fit your needs.

The program is a free download, has versions for Windows as well as the others, and does a huge amount of stuff if you climb the learning curve. For scaling and sizing, there's hardly any curve at all.

And being open source, they're not trying to sell you stuff, so there will be none of the annoying nonsense that Yonak mentions below That's probably my favorite thing about open source software.