Cobra and Super Cobra helicopters are two different breed of aircraft.
1. Cobra
Its the Army version cobra. It started as AH-1G, single engine back in 1966. over the years, it has developed into various models and last production model is AH-1F.
2. Super Cobra
Cobra helicopter was inducted in 1966 bu US army, straight in Veitnam war. US Marine Corps was so impressed with the capability of the helicopter, that they ordered a twin engine varient, of cobra, called AH-1J. As Marine chopper has to opertae over water, so they prefer twin engine varient over single engine. Over the years, this twin engine varient has undergone various upgrades. Now the production model is AH-1W, Super Cobra. The latest version of this family, AH-1Z, Zulu is in the procees of induction in US marines corps.
My Point--------> AH-1F cobra cannot be upgraded to AH-1W/1Z, super cobra, because of there fundamental difference (single engine / twin engine). It requires detail modification of fuseladge section, engine intakes, exhaust, trasmission system.
US Army has retired all its AH-1F helos, and using AH-64 as dedicated attack helicopter. USMarines Corps has no AH-64, and using super cobra. Please visit Janes site for details.
Pakistan Army Aviation, has initial batch of AH-1S(MC) or later renamed as AH-1F, 20 helicopters. Recently Pakistan has received 12 more, AH-1F helicopters. As of upgrades of anti tank missile system, Cobra is only designed to fire TOW missile, and cannot fire Hellfire missile as used on Appaches.