SQL Server/T-SQL Tutorial/System Functions/sp DropSrvRoleMember

A statement that removes a user from a server role

EXEC sp_DropSrvRoleMember JohnDoe, sysadmin

The syntax for sp_DropSrvRoleMember

sp_DropSrvRoleMember [@loginame = ] "login_ID",
                     [@rolename = ] "server_role_name"