Code:
select relat_to
     , sum( coalesce(q1_1,0)
          + coalesce(q1_2,0)
          + coalesce(q1_3,0)
          + coalesce(q1_4,0) ) / 4 as average_q1 
  from dbo.tbl_client 
 where relat_to='manager' 
   and group_name = 'MMColParam'
note you don't really need to GROUP BY on relat_to because your WHERE clause restricts it to only one value

rudy