You can use photoshop or even paint. I don't remeber how tho. I don't have to, I'm lucky. Good luck! 

You can use irfanview, too. It's a free download, and you just resize, and save as a jpg file. 

On the picture view window you can just crop it or you can set it to a preset size and choose "web". If using MS paint, then go to View on the tool bar, Size and then just adjust the size. Those are the easiest ways to do it. If you have a good digital camera, you can just adjust the settings also to a preset size.

Hope this helps