If you need help with resizing the picture let us know.

I usually use the Paint program that comes with windows and use the Image - stretch/skew
and reduce it by 50% and then more or less again until it looks about size of the avatars here.

Then do the upload & save part shown on moose's post.

It may say upload failed - but don't believe that - check it first yourself - look at one of your posts to see if the new avatar shows or not.