Read item 5 in this post ---> https://passionford.com/forum/viewtopic.php?t=1457

It tells you the sizes you must stick to.

then read here ----> https://passionford.com/forum/viewtopic.php?t=29894

Design yourself a Siggy and save on your computer.
You will then have to open a www.photobucket.com account and upload the picture there.

Once this picture has loaded it will have 3 links under it.
copy and paste the bottom link into the relevent section when editing your profile.

Hope thats of some help mate.