What you're using now is way beyond the height (150 pixels) and file size (30 MB) limits. Please remove it. Your best bet would be to check out the above link, and read through the threads here to see who is still actively making siggies, and which ones most appeal to you. Then you can PM those members, and ask them to make a siggy for you. They'll probably send you an email address, and then you should send them the photos you want included as jpg attachments. The files you attach can be large, as they can more easily work with large files, and then resize them.
Alternatively, you can start a thread asking who is willing to make a siggy for you, and see who responds.
If you'd like to resize yourself, try this freeware: www.irfanview.com