Make sure you are logged in to Galaxy.
Go to User > Preferences in the top menu bar.
To change email and public name, click on Manage Information and to change password, click on Change Password.
Make the changes and click on the Save button at the bottom.
To change email successfully, verify your account by email through the activation link sent by Galaxy.
Note: Don’t open another account if your email changes, update the existing account email instead. Creating a new account will be detected as a duplicate and will get your account disabled and deleted.