To change your Fortnite name, you need to change the display name of your Epic Games account. Here are the steps to follow:
1. Go to EpicGames.com and sign in.
2. Click on your username on the top right of the screen and select Account.
3. Go to the general tab and look for your display name.
4. Click the pencil next to it or the edit button to enter your new name.
5. Save changes and load up Fortnite.
You can only change your name every two weeks and you must have a verified email address . I hope this helps!