Hello,
In APO you have different reports to delete different kind of orders.
Most of the requirement orders (such as sales orders) can be deleted running report /SAPAPO/SDORDER_DEL.
You also have the report /SAPAPO/DELETE_PP_ORDER to delete orders related to production process.
And as Ada already replied, you also have the transaction /sapapo/rlcdel, that delete other type of orders.
I believe that in the following link you have more information on the orders that can be integrated with APO:
http://help.sap.com/saphelp_scm70/helpdata/EN/15/91b07822ad11d5b4010050dadf0791/content.htm
Hope that this could help you further,
If so, please set this reply as helpful and/or correct,
Kind Regards,
Luiz Giani