It's important to note that to upgrade weapons further, you'll need to upgrade your Gunsmith. Starting out, it will be labeled as "Gunsmith I," which means it's at level one. You can level up your Gunsmith by going to the "Level Up" tab inside its menu. Here, you can see all of the required resources you need to ARC Raiders Items advance the station to its next level. If you have the required resources, select "Level Up" and your Gunsmith will be upgraded.

Back to upgrading individual weapons, it works roughly the same as upgrading the Gunsmith. You can select a weapon from the Weapon Upgrades menu, see the required resources needed to upgrade it, and then choose to upgrade the weapon if you have everything you need.

If you're opting to upgrade a higher rarity weapon, like a purple or yellow weapon, then you'll need far rarer resources when upgrading it. Even if the weapons are at level one, they will require resources that match the rarity of the weapon's color. This is a massive investment, especially considering how difficult it can be to obtain those weapons in the first place. As such, it's highly recommended to only upgrade and equip higher rarity weapons on important drops or when you have a full team that's ready to get your back. There's nothing worse than losing an extremely rare weapon due to accidentally having it equipped, or when you drop in solo and end up dying.

Every time you successfully upgrade a weapon, it will move up a level. With every new level, a weapon will receive increased stats with no downsides. So there's really no reason not to upgrade weapons unless you're holding onto specific resources that you need for something else in cheap ARCR Coins. However, given how much of a difference an upgraded weapon can make, it's wise to prioritize stronger weapons over most other upgrades.