Absolutely! You can change your username by following these instructions:
- Tap Me icon (bottom right corner)
- Then tap on your username (3rd text field from the top)
- Enter the new username you want and press Done
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.