Are you using an editor like Dreamweaver? If so, you can just select the theme folder and search (ctrl+F) for About Me then change it.
If that doesn't work for you, check the theme options - Log into the dashboard then mouseover Appearance > click the drop down arrow. If there's Your Theme Options below the editor link, click it and see if there's an option for you to change it.
If there's no option to change it, click "editor". That brings up the theme editor. Your theme should be selected, but double check it in the top right corner > Then select the file from the list called sidebar.php or something similar probably.
Once the file loads, click inside the text editor box and search (ctrl + f) for "about me" (quotes not necessary).
If you don't see sidebar.php at first glance, double check. It looks like the standard wordpress template files are sorted alphabetically first then extra files are sorted alphabetically after that.