Where and how do you change your weapon in assassins creed 2

Pressing Up, Down, and Right on your Directional Pad (Cross) will select Hidden Blades, Fists, and Sword. To use any other weapons press RB (R Bumper, the little one) to access your weapon wheel.
To select among all the weapons and armor you already own, you need to go to your uncle's villa. On the left side of the first floor are two rooms containing all your weapons and armor. You go to the appropriate stand and then make selection.
As far as I can tell Ubisoft makes you go back to the Villa to change weapons and get your income just to make the game longer/more realistic and/or they are getting kick backs from the rapid transit merchants.