Create GIT users in our GIT server and delete some of them

We need to set up 3 new users in our GIT server (not github). We also need to delete some old users. We need a list of current users in our system, so we can confirm which one can be deleted. We have a dedicated linux server in 1and1 hosting, with root user access. FTP services are disconnected as we want. So we only use SFTP and SSH to log in. We'll provide SSH access to you, with root user, so you can perform these actions. Thanks, jc