I'd list all weapons in an array (weaponList), together with their current power (I'm guessing 1-3 is the power for each weapon, right?) so I could add as many weapons as I needed later. Also, I'd use a variable (selectedWeapon) to store which weapon is currently selected.
So I could use the following code to switch:
On <key> pressed >> Set selectedWeapon to (selectedWeapon + 1) % weaponList.Width
When shooting, I'd just check selectedWeapon and the power of that weapon in weaponsList, and create the blasts accordingly.