Upgrade

1. Overview
Upgrading will increase the level of car part by using Coins, as a result, their stats are boosted as well.

2. Rule
To upgrade, player needs to spend Coin. The required amount of Coins depends on the rarity of part and the level. As a rule of thumb, higher level and higher rarity need more Coins.
The rarity also affects max upgrade level. The higher the rarity is, the higher max level.
Also, NFT Parts will have a higher max level compared to other Parts.
Player can only upgrade part if it's crafted (i.e. the part is in a car)