To change your username on an Android device, do the following:
Steps to change display name
If you're using the Roblox app on an Android, iPhone, or iPad, you may have to click three dots instead. Click Settings on the menu. This will take you to the "Account Info" section of your settings. Click the Edit icon next to your username. Your username is at the top of the page, and the Edit icon is to its right.
You must have 1000 Robux to change your username. If you don't have enough Robux, you'll see a pop-up that says "Insufficient Funds.". Click Buy if you want to buy some Robux, and then follow the on-screen instructions to pay.
1. Log in to Roblox. If you're on a computer, go to https://www.roblox.com, enter your username and password, and then tap Log In. If you're on your phone or tablet, open the Roblox app (the black and silver diamond icon) on your home screen or in the app drawer.
Roblox now allows all users worldwide to change your Roblox account's display name in the account settings as a free feature. This is different than Changing a Username.
Log into your account (If you can't log in, try these steps for resetting your password .)
Your display name and username will be visible on Roblox and associated experiences
A ROBLOX Username is the associated name with your account when you created it. This is required to login to your account, as well being the unique identifier of your account. No two players can have the same Username, and as such, is completely unique.
Changing your username on ROBLOX is an easy, but expensive process. Changing to a new Username requires a cost of 1000 Robux to change, so make sure you’re willing to part with that Robux in order to amend your 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. This allows for players to be seen as their desired name, without incurring the costs like Usernames do.