Hi balasach82,
Lets say i have a job that is called Backup and my servername is BI-ONT this could be the query that you could use.
Update msdb..sysjobs
Set name = 'BI-ONT'+'_'+ name
where name = 'Backup'
If you don't use the Where clause de statement will update all your jobs.
Don't forget to refresh your object explorer after all of this.
Marbo