Instructions
Shoot an enemy with your starting weapon, the Walther P99 pistol, which Bond begins every mission with. Once you kill an enemy, he will drop his weapon.
Move over the weapon and press the "X" button to pick it up. You can carry a maximum of two weapons in addition to your P99 pistol. If you do not currently have two other weapons, you will automatically pick up a weapon when you walk onto it in order to fill your empty weapon slot.
Press the left or right directional pad to cycle through your current weapons. To switch weapons with one you find, equip the weapon you would like to switch, move over the desired weapon and press the "X" button.