SELECT 'EXEC sp_update_job @job_name = ''' + name + ''', @owner_login_name =
''sa'''
FROM msdb.dbo.sysjobs

Execute this, then copy the script from the result window, paste it into a
query window and execute the script.

If you want to execute it dynamically, create a cursor that loops through
msdb.dbo.sysjobs and one at a time select the string into a variable and
execute that using EXECUTE (@string_variable).

RLF