How to swap a specific weapon for a new weapon during a supply drop in MGSV: TPP

I currently have two primary weapons equipped. I want to change one of these primary weapons for a different weapon. I order a supply drop, and this arrives. How do I specify which of my two primary weapons should be replaced by the new weapon?


The two primary slots are for different types of weapons. The first is for your rifles, shotguns etc. and the second is for your heavy weapons such as the sniper rifles, machine guns and launchers.

If your supply drop is a heavy weapon it will replace your current heavy, otherwise it will replace your primary in the first slot.