Downgrading our gear isn't as bad it sounds. The stats remain the same. All it does, is lower the level requirement at which we can equip the item. At the end of the day, it just means we can use it sooner.

The Downgrade Merchant in each main cities sells some, below average, downgrade stones. Upon failure, our armor and weapons will disappear, completely. Hence we recommend using the ones from the cash shop. Not only do they have better success, but if failed, it'll up the level restriction by one -- instead of destroying our gear. The cash shop Armor and Weapon Downgrade Crystals are under the section "enchantment items" and they are tradeable.







Success rate
We should also consider the purchase of an Enhancement Charm, from the cash shop, to increase success rate. These charms are also tradeable and can be purchased from other players.

Downgrade stones from the merchant
While these have a lower success rate and will destroy the weapon upon failure, they can be a cheaper option if the weapon or armor is a piece we can easily get again -- if it can be crafted for example. A good way to know if we want these stones or not, is to think about the work we'll have to re-do to get the gear back. For instance, if it's a modded or golded armor, we're better off with downgrades from the cash shop. Because re-modding or re-golding our piece would be too costly.

Downgrade items
Armor downgrade stone, from merchant
Armor disappears if unsuccessful

Weapon downgrade stone, from merchant
Weapon disappears if unsuccessful

Armor downgrade crystal, from cash shop
Increases equip level restriction if unsuccessful

Weapon downgrade crystal, from cash shop
Increases equip level restriction if unsuccessful

Bronze enhancement charm, from cash shop
Success rate +10%

Silver enhancement charm, from cash shop
Success rate +20%

Gold enhancement charm, from cash shop
Success rate +30%

Once ready, click the downgrade crystal, then add armor or weapon. In the same window, add the enhancement charm and click confirm. This can be repeated for a total of 5 times.

• Original pictures from wiki[domo.fandom.com], edited by me
  
• Armor tooltip screenied in-game and edited by me