Give Admin to Players for Garry's Mod

Find the SteamID for each person you want to make admin. You can use a website such as https://steamid.io/ to lookup a Steam user to find their SteamID.
Login to Command Center.
From the servers page, click the Manage button for your Garry's Mod server.
Navigate to the Files tab seen above the console.
You will see all of your server's files on this page. Navigate to /garrys-mod/garrysmod/settings.
Click on users.txt inside the settings folder. This will open the file in a separate window so you can edit it. If you'd rather use your own editor, you can use our SFTP instructions to connect to your server and open the same file with your favorite text editor.
Put your Steam Name then your SteamID between the brackets { } for either Super Admin or Admin.