Throwing hundreds of thousands of pesetas at upgrading weapons is a thing of the past in the Resident Evil 4 remake. The Resident Evil 4 remake, like the original, features the ability to upgrade weapons by speaking with the roaming Merchant. Players can choose from one of four stats to upgrade each time: power (damage), ammo capacity, reload speed, or rate of fire. Each upgrade costs at least a few thousand pesetas, and the higher level the upgrade, the greater the cost. However, since there are some 28 weapons to collect, most weapons will be replaced by superior versions at some point in the game, so it's not necessarily worth fully upgrading the first shotgun, for example.

https://screenrant.com/resident-evil-4-remake-weapon-exclusive-upgrade-ticket/