If I remember right, ya go to your PROFILE the word in the green bar. On that page there are various things you can edit, one of them is your SIGNATURE. That's the one.
Once you have changed it, it sends you right back to that page. Don't think you've done something wrong. Just go to your favorite news site and read and reflect a bit. Then, come back here!
I found it. It was under "personality". I didn't think I had one of those.
Actually I won't be 81 till May 7 but I was just trying to figure it out. Since I was already there I changed it even though it's a month early.