You want the "How To" section of the forum, right up at the top above General Ramblings. Basically, our forum moderator Wendy has to make all the changes to sig and avatar (long story). She's been very good about this, just send her a PM and ask politely.
Maybe we should have a "sticky" here in this forum, because everyone
(it's not just you, Flapjack) seems to miss the "How To" section!"