Sure you wanna know, Tx?? Ok.....
You'll need a hammer and 1 or 2 pry bars, as thin as you can get, but strong enough lift the claps to pull the nails. This kind:
http://visual.merriam-webster.com/house/do-it-yourself/carpentry-nailing-tools/pry-bar.phpAt times I also use a painter's 5 in 1 tool...it can be used to grab nails as you lift claps.
Cut any caulk lines on the clap you want to remove so it's not "glued" to anything. And on the one above it, also. This is mandatory, you'll break things if the board can't move. Gently get the long part of the pry (or 5 in 1....I often start w/that) under the row ABOVE your subject clap. Just enough to pop the nail...move to the next nail over the subject clap. Pop as many as you need, and you can work back and forth to get them high enough to grab w/prybar or hammer claw to remove. Use pry block if needed to not dig claw into your clap...go slow and easy.
If the nails flex back into their holes all the time and won't come out, you have to reach up with the 2nd pry bar and push the nail away from its hole as you allow it to sag back into the house...so the house kind of pushes it out as the clap snaps back....it's a technique that takes practice. The upper (keeper) clap can flex a little, but don't over-do it...remember the tongue up under the NEXT clap that you want to not break...
You DO have to disturb the row above to remove a clap....the one you want is nailed thru by it.
Once you have the area above free of nails, next remove them from the subject clap. This is easier as you can destroy this clap with no hurt feelings, lol. Remember that the one BELOW it is also secured with those nails, tho, so go easy so as to not break the fine tongue of the lower clap as you remove subject clap. Once all nails are out of the subject clap, you can slide it down and out pretty easily. If it won't go...look for stray nails. Sometimes they put one in a place you wouldn't expect, like up under the next row...to hold it in when starting or something.
If you are only trying to do ONE clap and think that's it...and you haven't done this before...I highly recommend you find a carpenter that's done it, give them $50 to remove it for you. This is surgery. You can EASILY wind up having to change 5, 6 pieces of siding if you're new and dive right in. They are delicate, and require a finesse that you have to LEARN, can't just pick it up. It's a system to learn like any other, at first it seems senseless but later you're like "OH, I GET IT"... But you might be able to get it down, who knows?
There are vids on Youtube about this, too, but usually on new houses where nothing is utterly stuck..
** Prime all 6 sides of new clap, and butt end of old claps before re-installing..... ** You'll be sorry if you don't, ha ha.