Username
You set your username once, the first time you log in. You can't change it after that.
To set it: tap Settings, then User Profile. Enter your username in the box and save.
Email address
You can't change your registered email address in the app. Chat with us in the app (Settings > Help & Support > Live Chat). We'll check that the account is yours before we help.
Phone number
You can't change your phone number in the app. Chat with us in the same way, and we'll help.