I accidentally put the wrong username for the github host account linked to my sourcetree and I cannot reset the username... I am only given the option of reinputting a password but not a new username. I have reset my cached passwords and have even added the actual username (Sourcetree > Settings on the top right > Remotes > Double Click on Repository > Add username). I still get the incorrect username to populate when I try to push the commit.
If you are having errors pushing then it is an issue with your GitHub account and you probably want to open Tools/Options/Authentication tab and edit or delete and recreate your GH credentials their.
If it is about the author information used in your commits, then you want to reset that information in Tools/Options/General tab