T-SQL :
update TBL
set picture = Replace(picture, 'servera', 'serverb')
where picture like '%servera%'
Oracle :
update TBL
set picture = replace(picture, 'servera', 'serverb')
where picture like '%servera%'
MySQL :
update TBL
set picture = REPLACE(picture, 'servera', 'serverb')
where picture like '%servera%'