Maintenance plan delete backup
Bob,

I am NOT a big fan of maintenance plans and I try to avoid using them. While they work ok for small needs it becomes hard to customize them but some ppl disagree with that. 

You need to look at the Maintenance Plan cleanup task. Make sure you enter the extension as 'bak' without quotes instead of '.bak' without quotes. The following two articles will help for you. Let us know if you need further help.

http://msdn.microsoft.com/en-us/library/ms177182.aspx

http://www.bidn.com/blogs/BradSchacht/ssis/249/sql-maintenance-plan-doesn-t-delete-backups