Um...looks like a pretty-straightforward trip lever design. I have three of something similar. Not identical, but similar.
Pull the cotter pin and slide all the loose pieces off the part of the shank that's protruding into the tank, and set them aside. Pull the handle and now-unfettered shank out the front, so now you're left with the trim flange on the front of the toilet, which is screwed into the fork nut inside the tank. In most toilets, there is a square hole in the tank, so the fork nut's square piece is going to lock, if you will, into that hole. I.e. when it's tight, you usually can't turn the fork nut because the tank is holding it tight. So you want to unscrew the trim flange from the front.
You do know, don't you, that toilet handle hardware is reverse-threaded? That is, instead of lefty-loosy (i.e. counterclockwise to unscrew) and righty-tighty (i.e. clockwise to tighten), you turn these things in the opposite direction of what you're used to. That's why the instructions say (#8) "turn counter clockwise until tight". That is, turn left until tight, which would normally loosen something screwed into a nut; here, it's reversed. Also, you normally just make this stuff a little more than hand-tight, so it shouldn't be that hard to turn once you're turning it in the correct direction. Of course, you may have been forcing it in the wrong direction, so now it may be a little tighter.
So, just take a rag or something and grip the trim flange, and, looking at it from the front of the tank, turn it to the RIGHT (Clockwise) to loosen it. You should be able to get enough leverage to get it started, and then the whole thing will unscrew. If you're not concerned about damaging the trim flange because you're going to chuck the thing, just grab the flange with the channel locks and turn it CLOCKWISE to loosen. You might want to have grabbed the fork nut with pliers on the inside and hold it so it isn't twisting against the porcelain while in the square hole. Then use your hand to spin the trim flange the rest of the way.
Again, do this AFTER you have pulled off all the pieces of the trip lever assembly that are inside the tank and then pulled the handle out from the front so all you are dealing with is the trim flange and fork nut.
Come back here if you can't get it to go. Actually, regardless, let us know how you make out.