You can view your profile information several ways, among them clicking your "Welcome" name in the upper right corner of the page, or clicking you name in one of your posts and selecting "View public profile". The "About Me" tab is one of the tabs in your profile.
When viewing your OWN About Me tab, you can edit several of the fields by clicking on the little pencil icons (
) beside the editable fields.
There is more information shown for your own profile than you see when viewing somebody else's profile. To see how your profile looks to others, click the
View your "About Me" as seen by everyone else link. The information you see there is fixed and cannot be edited. To return to your own "normal" About Me tab where you can edit your data, click the
Edit your "About Me" link.
Alternately, you can edit the same data via your User Control Panel (UserCP link in the blue bar near the top of the page).