By replacing the seal, you'll see how it works and can make any adjustment then, but I don't even think there is any adjustment.
How To Replace The Seal On A Canister Style Flush Valve From Kohler - YouTube
If your toilet looks like the one in this YouTube video, it's a real easy job to replace. (Except where he turns the plastic part at 42 seconds) It turns hard and you think you're going to break it. Also for those that are unfamiliar with the cheap plastic water shutoff valve. You turn the water off by pulling the white knob straight out.
Kohler K-GP1059291 Canister Flush Valve Seal
Last I knew was $6.99 at Amazon and about the same price at hardware stores. Make sure you get the yellow one made of better material than the original red one.