To change your Roblox username login to your account and go to the settings section. In a browser this is represented by the gear icon in the upper-right corner.

Roblox is finally letting its creators adopt a much more lax chat filter that allows strong language in their user-made experiences.

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.