I just got done doing this, what a nightmare. Anyways, whenever I need to know how to do something on the bump, I go to the board "new to the Bump." There is a girl that always responds to questions like this. She tells everyone to look at her profile and she has a step by step process for anything on the bump. It has helped me out a lot!
Re: Edit my siggy?
Arrrrgggghhhh I know! TheBump/Knot/Nest hasn't done a very good job of keeping this user-friendly, nor are they consistent with their changes.
Here's how I found it:
Go to "My Bump" top navigation bar
You should see your little profile thumbnail photo. Right about that is "Edit my Avatar" That's where they've hidden your siggy editing...
The Baby Blog.