1. You can change your in-game user name (nickname) by clicking your Stumbler avatar from the home screen.

2. Then click on the pencil icon beside your nickname.

3. Now you can write the nickname you want. The first time you change it is free, but then it will cost 100 gems every time you want to change it. 

4. Make sure to check if your picked name is already taken. 

5. Also check the character limit (4-12 characters long).