You can Ascend your Sorcery Card to increase its max level. The first Ascension costs Coin, but subsequent Ascensions will require Ascension Materials. You can get these Ascension Materials from the Oak of Deep Sorrow, and they each Calling has unique Ascension Materials that are needed to Ascend Sorcery Cards of that Calling. The Oak of Deep Sorrow rotates each day, dropping unique Sorcery Card Ascension Materials on each rotation, but on Saturday and Sunday, all Oak of the Deep Sorrow arenas are available.