To change your character's nickname, you may purchase a "Character Rename" in the "Boosts" section of the Item Store.  You can open the Item Store by pressing "," or selecting "Item Store" in the menu at the top-left of your screen.

Please ensure that you follow the Rules of Conduct when selecting a new nickname.  Once purchased, you will be prompted to enter your new nickname the next time you log into the game.

Note: this service does not change your character's first or last name.