Reference article
Equipment Upgrades
Spend coins to improve a weapon, hat or costume up to equipment level 5.
Buying an upgrade
Open the item in the inventory and use Upgrade. The price is the item’s catalogue cost divided by three using integer division, then multiplied by its current equipment level. For example, the 
Mallet has a cost of 30, so its level-1 upgrade costs 10 coins.
Stat changes
Each weapon level adds 20% of the original integer damage stat. Each armour level adds 0.05 to every protection value. Level 5 is the highest equipment level. Equipment levels are separate from the duck’s combat-skill levels.
Reward equipment
Some exploration and quest rewards arrive above level 1. Their individual articles record verified starting levels.