Well trade, gamble etc etc while you still have a servant, or summon a new servant with the card. Then you could even win another Arcana minor card of a different class, and use that as your base when you go to upgrade it to Arcana Major.

Also if a servant can fit multiple classes, they can bind to many different Arcana cards, although they will be strongest is used with the card under the class they were summoned. 

And I'll do the Opening post.