To get or change a Roblox Display Name, you should first log in to your Account Info page under Settings, then select the edit button next to the Display Name entry above your Username.

How Can I Change My ROBLOX Display Name? You can change your Display Name for free, once every seven days. This is how other players see you in-game and isn’t unique to one player.

The process for changing your display name on Roblox is fairly simple. Here's a full breakdown of how you can change your display name in Roblox.