How to overwrite existing DB's in SQL 2008?

I use Maintenance Plan of SQL 2008 Server for Backup some DB's. As a result i need to keep, only one set of Backup Up's and not more. So actually i can use Maintenance Plan Clean Up wizard, but i need something like Overwrite. That mean i don't want do delete DB's after i finish Backup UP, but i want to overwrite existing backups?

Thanks.