How to delete packed outbound delivery

Hello gurus.

I need urgent help. I want to delete the outbound delivery that is already packed. Namely, I have one outbound delivery that contains 10 materials which half of them already picked that is TO was created and confirmed. Now I want to delete outbound delivery but system gives me error message VL173.

Please give me advice how to delete outbound deivery in my situation ?

Thanks beforehand.