Do the water temple first, then the tower of eternal flames. You are more than ready.
You do not need a ring of ice. A fireproof blanket is all you need. You do not need slaying ammo either. Throw a blessed potion of cure corruption at the Wyrm, that will deal very high damage and eliminates his corrupting attack. Next, you can kill they wyrm using whatever your best damage option is. Demon slaying and dragon slaying ammo both work, but spells and melee work too. You do need a way to protect yourself from confusion. Equipping the water orb helps (willpower bonus). And stay healed, never let your health drop to a point where an energy ray can kill you.
You steal a scroll labelled HITME. The orc hits you.