If you are playing through sinlgeplayer campaign you can get fairly early on. As you are playing through the game you will start to get gear that is green different colors (colors represent rarity). Any color besides white can be upgraded. When you start to get them you will get an in-game prompt saying you can start upgrading gear. to upgrade your gear you press
then go over to the gear tab move your cursor to the desired gear item you want to upgrade (note: you have to have the correct amount resources to upgrade it which can be obtained through playing mission, opening chests, destroying resource boxes, and killing enemies) once you are hovering the desired gear if you have the right resources hold
which will upgrade it. You may have to upgrade it multiple times which you will see a bar on the gear description that will go up with each upgrade. once that is filled the achievement should pop.
Please message if you have any questions. If you down vote please let me know why so I can make the solution better.
-Happy avenging