If I gain a spell and I olready have the full amount of spell can I take it and choose witch one to discarded??

Hamal22 said:

No, other than casting it you can't get rid of a spell you currently have unless a card or space specifically instructs you to. So if you already have your full complement of spells that your craft allows, you can't gain another one and simply wouldn't draw another spell card when instructed to do so.

Actually if you have a spell that can be cast at anytime then you can get a new spell, for example if you have Invisibility then you can cast it and then gain a new spell with the card.

frogemoth said:

Although it is reasonable to allow this as a house rule, no Spells can be used in the middle of another action. When you gain a Spell, you must be able to take it at that moment, otherwise you don't get anything.

Spells that are cast "at any time" don't have a specific timing during the turn, but it's not possible to cast them when you're resolving another action.

Example: if you land on the City and roll for the Enchantress, if you want room for a new Spell you have to cast something before rolling the die. If you roll a 6 and cannot take a new Spell, you don't have the time to change your mind.

These are not rules given by the Rulebook. The basic Rulebook has enough rules for the basic Spells only. But ideas such as "Spells must be cast before a die is rolled, not after", which are spin-offs from similar rules (i.e. combat rules) have been discussed for so long that they're like rules. I'm still hoping for a FAQ update that features a comprehensive section about Spells.