I'm not sure if this is right, but I think it might be: There's an option on the Photobucket website that lets you standardize the size of all of your pictures. Let me see if I can find the link. Actually, I think it might be one of those premium options that you get for buying the yearly service, but I'm not sure. Let me check.
Try this link. See if it helps:
http://support.photobucket.com/hc/en...d-Size-Options
If that doesn't help, then when you're editing the pictures, make sure to click on the box that says "Replace Original." That might help, but again, I'm not sure.