You can change the tier of your Crypto Prophets by collecting 5x Crypto Prophets of the same race and tier and then burning them using a burn spell (available from the store).
By casting the burn spell you will summon a new Crypto Prophet of the same race but in the next tier up.
Base cards
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New card
5x Common
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1x Uncommon
5x Uncommon
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1x Rare
5x Rare
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1x Epic
5x Epic
=
1x Legendary
You can not mix Prophet races or generations when burning, so all prophet cards must be from the same race and the same generation.