To upgrade cards you need to have collected some "Dust". Refer to consuming section to find out how to collect said "Dust". Once you have enough "Dust" in your possession click on the card that you would like to upgrade and the screen will change to show you all the possible upgrades for the card typically it chooses to show you the stats of the card once you upgrade it one level. To upgrade tap the "Upgrade for X" button (X standing for the amount of dust it will cost to get to the next level). That amount of dust will be infused into the card increasing its level by one therefore also increasing the cards stats. As the level of the card increases so does the amount of "Dust" needed to raise it to the next level. The rarity of the card also determines the amount of "Dust" needed. Bronze needing the least, then Silver, Gold, and finally Diamond. Once the card has been upgraded to level 5 the "Upgrade for X" button will change to a "Fuse" button.
All cards start out at level 1 with some base stats. Under the Research area, you will see an Upgrade option, where you can recycle cards into dust to give "experience" to other cards. After using enough dust, the level of the upgraded card will increase by 1, increasing its base stats by a set amount, shown below. There are a few exceptions, but these are the general amounts.
Stat Increase per Rarity
|Rarity||Increase per Level|
Consuming cards is the process by which you sacrifice existing cards that you own to receive "Dust". By consuming the chosen card you are able to increase your total "Dust" amount. To consume card you must be on the consume screen after entering the upgrade card screen. You can access the consume screen by tapping on the little plus button in the top left corner next to your total amount dust. Once on the consume screen you can then tap on a card to place into a recycling spot. A dialogue box will appear showing how much dust you will collect if you choose to sacrifice that particular card. If you decide that you want to consume the card and receive the allotted dust then press the "Recycle Card" button which will then display an animation of the card being converted into "Dust". The maximum amount of dust that you can have in your possession at one time is 500. You will not be allowed to consume any more cards until the number is reduced below 500 where upon you can then begin consuming cards again. Keep in mind that cad that the cards you consume cannot be retrieved so check the card before hitting the "Recycle Card" button.
As card levels increase, the number of cards required to increase their level further approximately doubles. Experience gained beyond what is required for the level is carried through to the next, causing a Bronze Upgrade (6 Dust) to give a Lv 1 Bronze card ~1.25 levels. The tables below use Lv 1 units for consumption, but experience is lost when using higher level units i.e. if you recycle a Lv 2 Bronze card, it provides as much dust as a SINGLE bronze card ( a quarter of 3+1 ).
Despite the change to dust, the amount required per level of card is still approximately the same for all rarities.
Also of note, if prior to 1.25.3 you had used cards to partially level up a card, or had overage from an Upgrade card, the cost will be deducted from the cost to raise the card to the next level.
Dust per card
Note that pre-dust cards may vary from these values; it looks as if they've saved how much went into the upgrade process.
Dust Required per Level per Rarity