You exit the server you are currently in and go to a different server (that's not already full) and click the join button.
Chat with our AI personalities
What do you mean? And you change the name of the models on Roblox Studio.
To change your outfit on Roblox you must have an account (not be playing as a guest). First click "My Roblox". Then click on "My Character". From this page you will be able to customize your Roblox character with any clothes you have bought in the game.
If you are referring to the servers in a game, just go to the page of the game and scroll down until you see a grey bar with the word 'Games'. Click on it and below there will be the list of servers in the game right now.
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Change the country your from in settings.