Kalen,
You will need to access the database, which is not difficult if you have cPanel hosting or other phpMyAdmin access. Open the Moodle database (probably named _mdl, _mooxx, or similar), find the mdl_user table (or mdlxx_user, but always _user), click that file name, find the capitalized user, edit, and save.
This should work, although more seasoned users may have a better method (or offer clearer instructions).
Ken
I realize that this thread is a little dated now, but I'm having the same problem, where I'm unable to change the profile of the admin because of the capitalization of the username. My Moodle was installed by Softaculous.
I've looked at (searched) the files in the cPanel but can't seem to find the one what contains the name to edit it. Ken's description pointed me in the direction of a solution, but I can't seem to find the file. If anyone can be more specific, I'd appreciate it.