The Kohler Kelston is a two-piece unit, consisting of an upper tank and lower bowl. The water fill valve on a Kelston isn't remarkably different from other toilets. Adjusting the water level simply involves turning a nut at the top of the fill valve. The Kelston does use a flush canister, which is somewhat different from simpler models that use just a flapper and chain for flushing. Still, adjust the chain or replacing the seal on a Kelston is still relatively easy.
Check the Water Level
Lift off the tank's lid and check the water level. If you see water draining into the overflow tube or reaching the level of the overflow tube, the water level needs to be adjusted lower. The water should come about an inch below the top of the overflow tube. If it's too high, the water will never shut off, causing the running sound. To adjust the water level, twist the thumb screw at the top of the fill valve's rod counterclockwise. The rod should lengthen by about an inch. You'll have to experiment with a few flushes to ensure you get the adjustment right.
Food Coloring Test
If the water level in the tank is OK, you may have a leaky flush seal. Put food coloring in the tank and don't use the toilet for several hours. If you see the food coloring in the bowl, then you have a leak.
Replace Flush Seal
To replace a leaky seal, turn off the water to the tank at the shutoff valve behind the toilet. Disconnect the chain from the flush lever and turn the canister counterclockwise one-quarter turn to remove it from the tank. Turn the canister over and remove the rubber seal, replacing it with a new one. Return the canister to its original position in the tank, reconnect the chain and turn the water back on.
Adjust the Chain
The chain should hang freely from the flush lever and extend to the flush seal. There should be a small amount of slack in the chain. If the chain is too tight, it might be preventing the flush seal from keeping the water in the tank. If it's too loose, some of the slack may have gotten caught in the seal. You can make the chain longer or shorter by selecting a different chain link to attach to the flush lever.