Kingdom Hearts 2 Question. . .?

I'm up to battling Demyx in the game Kingdom Hearts 2. It's a little difficult for me to finish him off; I've tried a few times but lost due to the ten forms in ten seconds thing, and his cheesy stupid attacks near the end of the entire battle. I have some anklets and rings and other special items I want to use; are they automatically equipped, or do you have to manually equip them for Sora? I want to have stronger MP and defense when battling him, but how do I do that? Thanks. . .!