Well you have some options:
1. You can learn how to use a graphics program and focus on changing the actual pixel size rather than just the overall kb size. Then save your FP and upload again.
2. You can upload in the Forum Gallery which allows a much larger output, you can actually upload several pictures, but unfortunately none will appear as your avatar.
3. You can upload to our Hot or Not Gallery, but that does not show as your avatar either, but it is fun to get your photo rated.
4. You can
donate to the Community as I believe one of the Upgraded options allows you to get your photo sized and installed by myself.