Slowly raise the temperature to 30c. One tablespoon of aquarium salt for every 20 litres of water. Make sure you keep this up for a least a week or 3 days after the last signs of ich have gone whichever is longer.
The ich parasite cant be killed while it is infecting your fish. It can only be killed while it is in the freeswimming stage of its lifecycle. So if you dont continue the treatment after the visible of signs infection have gone, your water will no longer have the medication/salt present during this freeswimming stage and the ich parasite will still be present in the water to reinfect some time in the future.
Also note that there are salt resistant strains of ich, so salt may not work and you may needs meds to clear it up. Also note that some things in your tank may not tolerate salt, eg plants and some fish. What do have in the tank?