We hear you. Sometimes we start playing a game without putting too much thought into what name we would like to identify with, ending up with one we don't like.
If you are not satisfied with your nickname, you can change it following these steps:
1. Tap on the menu image on top right conrner
2. Tap on the "Settings" button
3. On the new pop up window, tap on "Change name"
4. You give your new name and tap on the "check" button to the right
Please keep in mind that you can change your nickname for free only once every six (6) months and for 100 Gems every one month since your last change.