Trying to work out the best process for when a supplier sends a replacement part for the original part ordered on po.

So far:

1. Part A added to order
2. PO created for Part A and sent to supplier
3. Supplier sends Part B in place of Part A

Questions:

1. When receiving Part B
   1. do we have to add Part B to original order? And then zero out Part A?
   2. do we have to add Part B to PO and zero out Part A?
   3. then receive Part B?

I am sure it is a very easy but I have gotten myself extremely confused and thus looking for clarification.

thanks