Yes, temperature alone can kill ich, but temperature + salt will do a lot better (especially because it sounds like the disease is in an advanced state, since it already killed a few fish). As posted earlier you can add 2 tsp per gallon, or if you buy actual aquarium salt, follow the instructions there.
This is how you should be doing it:
Take out maybe 25% tank water, just like a water change
Fill a container with enough tank water to replace it
Add 2 tsp per gallon
So if you have a 10gal tank... and you take out 2.5 gallons, then you want to add 5 tsp of salt to the water you will put back in the tank. Just keep doing this (every 4 hrs or so, or once a day) and you will slowly raise the water's salinity to the desired level.