Roblox allows all users to change their Roblox account's display name in the account settings without spending a dime. Here's how to do it.

Steps for altering your avatar’s appearance in every Roblox experience, from adding and removing items to changing your skin ...

ROBLOX allows you to change this username, as well as your Display Name. It’s important to note that there are different rules and applications of both Usernames and Display Names.

Gamertag, username, display name; a Roblox player has multiple names, each having a purpose. Thankfully, usernames and display names chosen years ago can be changed.