Absolutely! You can change your username by following these instructions:
- Tap the menu (from top left corner)
- Then tap on "My account"
- Next, click on the existing username to start the edit process on the next screen.
- Enter the new username and press Done (or click the check mark) to apply the changes
And it will save your new username!
If you get an error message, it's because all usernames must be unique, someone may have already registered with the username you are trying to get... You will need to change it to a different one.