Easy way: (Assuming you have Windows 98 or later)
Pull up the picture before you get on line. Put the mouse arrow over the picture, and 'right click' with your mouse. You should get a drop-down menu. Select the 'Save picture as...' option by clicking on it. Save it to your desktop in a Bitmap (.bmp) format.
Close any open windows, and pull up the .bmp picture-- it should come up in 'Paint'. Now go to 'image' (upper left) and click on it. Select 'stretch/ skew' from the drop-down menu, and where you see a box with '100'% type in '50'. There will be two boxes, one for vertical and one for horizontal-- do this for both. If that's not small enough you can do it again. If you mess up you can go to 'edit' and select 'undo', or even close out completely without saving changes and just pull up the original and start over.
Resave the image in .jpg format when you're done. You can also use Paint to crop your image by selecting the little square on the upper left menu and playing with it.
Hope this helps!