Change of resource type in APO

Hi,

I want to change the resource type (multi mixed to single mixed ) of some resources in APO.

I can see that the resources are already linked to some orders and to PDS which I don't need further because of which it is not allowing to delete the resource.

What is the best way to do the delinking of these orders and PDS and to send the corrected resources from ECC?

Could you please explain explain step by step procedure to do this.

Thanks in Advance...

Prash