If you want to try to upgrade your NFT, you need to choose NFTs to use them for the upgrade. More NTFs = higher chances to upgrade.
You cant upgrade basic NFTs
Be aware — if you fail your upgrade attempt, you will lose half of used NFTs. If your attempt is succeeded, then you will get NFT with better rarity, all used NFTs will be burned.
You can upgrade: ❄️Normal -> Rare (if upgrade is successful you will get 6 rare!) 1 NFT = 10%, max chance = 90%
☃️Rare -> Legendary (if upgrade is successful you will get 2 legendary!) 1 NFT = 10%, max chance = 90%