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Once the set screw is out the handle should pull right off. However it's not uncommon for the handle to seize onto the stem. You can try injecting white vinegar into the hole the set screw was in which may break the handle loose after it sets a while and/or work the end of the lever up and down until it loosens up
Give it at least an hour. You may have to do it several times. Before you try to take the handle off give the end of the lever a rap up then down a couple times with the handle of a screwdriver to try to jolt it loose.
You back off that knurled collar that's at the top of the handle base. Once that's off you lift the base off and you'll see the stem which will have a hex or wrench flats to back it out. Turn the water off first of course
remove the stem extension then unscrew the collar below it. Here's a link to the install instructions wit the parts blow up on page 12 & 13http://www.us.kohler.com/webassets/kpna/catalog/pdf/en/1117155_2.pdf
probably seized up too. Try the vinegar again
The screw into the top of it holds it in place. It should just pull off the cartridge stem.
yes but it looks like you have to get the collar off to access the hex on the cartridge to get it out
Put the vinegar at the base of the extension. If you can get to the hex on the cartridge you can take them both out together but you'll have to get the extension off eventually or replace it. It looks like the collar has to come out so you can get to the stem hex
Back off the hex at the base of the stem
Looks like it's in the right place (the hex at the base of the stem). You won't see a hex like this on a faucet part unless it was made to be turned. Try more vinegar or PB Blaster (at Lowes and HD).
WD 40 is not designed for this type of condition. You can remove the entire faucet by disconnecting the water lines under the sink and backing off the lock nuts holding the faucet in place. I doubt it will make any difference except perhaps that you can immerse that side of the faucet in vinegar.