Easy enough.
You get pieces of armour during the game. Pressing the touchoad brings up the menu, cycle over to the inventory.
As you go through missions, you'll find big boxes you can ounch to get upgrade components.These also drop off enemies ebery now and then, also from lockbox caches.
On the inventory screen, you can destroy rubbish equipment for more resources by hovering over it and holding
Then upgrade the piece of equipment you want to use by using
some will require 3 upgrades, the better the equipment the more upgrades you may need.