how do I upgrade my characters and cards?

click the card you want to evolve, at the right side of the XP bar you will see a button with 2 cards and a green arrow, click it, you will see the upgrade screen

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I did that and nothing happened it just does nothing

You also need to play with them and gain XP by them. Once the red XP bar is filled, then and only then you can upgrade them.
(Remember, some upgrades needs the fusion of more than one card!)

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