This is what elemental Keyblades will do to spells. Remeber you have to have the specific element for it to apply:

Fire Spells:

Fire 1/2 MP - Description: A medium blast of fire.
Fira 1/2 MP - Description: A thick shield of fire.
Firaga 1 MP - Description: A very powerful fire blast that can be either fired at one's opponent or made into a shield that knocks away enemies and attacks.

Blizzard Spells:

Blizzard 1/2 MP - Description: A medium blast of ice.
Blizzara 1 MP - Description: A large blast of ice.
Blizzaga 2 MP - Description: A powerful ice blast that freezes one's opponent for two posts.

Thunder Spells:

Thunder 1 MP - Description: A medium bolt of lightning that isn't that fast, but isn't slow either.
Thundara 2 MP - Description: A large bolt of lightning that's fast.
Thundaga 3 MP - Description: A very large bolt of lightning that is very fast, and if it hits, one's opponent is stunned for two posts.

Cure (Light) Spells:

Cure 1 MP - Description: Rejunvinates the mind allowing two double posts during the topic.
Cura 3 MP - Description: Rejunvinates the body allowing two of your opponent's attacks to be negated.
Curaga 5 MP - Description: Rejuvinates the mind and body, allowing you to get one major hit undone. So if it was a fatal blow, and you used this spell before hand, you can undo it.

Aero (Wind) Spells:

Aero 2 MP - Blocks two attacks that uses a weapon.
Aerora 4 MP - Blocks two attacks that uses Magic.
Aeroga 6 MP - Blocks three attacks that use either weapons or Magic.