Q: Need to add a device to itunes account, but must delete 1 or 2 old ones first, How?

I need to add a device to my iTunes account, however in my account it indicates I have 5 computers associated with the account already.  I need to delete 1 or 2 old computers associated to the account.  The only option I can see in manage my account is to diassociate ALL computers...how do I delete just 1 or 2 old ones and add the new one?