Backup and delete backup windows 2008 r2

Hello.

I want to use backup of win 2008 r2 (wbadmin or gui interface) and i have several doubts.The policy i want to implement is that I backup copies to be made fullon fridays and incremental from Monday to Thursdayfor six months, after which it erase everythingand start over.Do i need to tell to wbadmin if is it full or incremental?In afirmative case we should create two tasks and how to? How i delete all backup automatically to free disk and start again? Thanks.