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"