Cannot figure out how to take apart the lever and

This is called the diverter if it is a tub/shower valve. There are just too many brands to say just how it comes out. Remove the handle. You may need a handle puller. Remove the trim. This varies. If I had a picture, I could tell you how to do this. You will then probably need a deep plumber's socket to remove the stem. Make the stem is turned all the way counter clockwise before unscrewing the stem. Go to a good old time plumber shop or hardware store to get a new stem.

follow this steps and fix it. God bless you
Service a compression faucet:

1. Turn off the water supply and open the faucet handle to relieve water pressure.
2. Carefully pry off the trim cap with a small screwdriver or putty knife.
3. Remove the locknut with an adjustable wrench, then lift the spindle out of the faucet.
4. As needed, remove and replace the O-ring. Before reinstalling, coat the stem lightly with plumber's grease.
5. As needed, remove the retaining screw and pry out the washer. Install an exact-replacement washer and tighten it.
6. As needed, inspect the seat and replace if damaged.
7. Install the valve and tighten, then reinstall the handle and test.

Repair a reverse-compression faucet:

1. Turn off the water supply and open the faucet handle to relieve water pressure.
2. Carefully pry off the trim cap with a small screwdriver and remove the handle screw. Unscrew the packing nut and lift out the stem assembly.
3. As needed, pry out the washer under the packing nut and replace it.
4. As needed, remove the seat washer and replace it with one that fits exactly. Rethread the spindle and washer back onto the stem, and reassemble the faucet.

Thia video will walk you through it. Your faucet may be a little different.

http://www.youtube.com/watch?v=AipEYoYiIhc

Will need to get delta faucet rebuild kit. Available at home depot, lowes or hardware store. It consists of valve stem seals & springs. The larger kit will contain ball assembly. Turn off water to faucet. Unscrew handle via set screw under plastic cap. Unthread cap over ball assembly. Pry out valve seals & springs. Reverse procedure to install.

Faucet is leaking due to seats bad.

1- Turn water off first and remove handle and remove collar that holds stem and remove it..

2- in valve there are seats that looks like caps they may be in valve body or the end of stem itself.

3- Remove them and the springs and replace them this will take care of the leaking problem.

1- Hanldle may have a cap that will come off to access screw to loosen or allen screw on the handle to remove it.
First thing you can check remove handle and make sure the nut that holds stem down is not loose. You can tighten it and try this first just replace handle turn on and check for leaks.

If not please go to step 2 in removal of stem

2- Cut water off and remove handle to gain access to stem. Next remove stem by untighting nut at the base. Remove stem and replace o rings on stem about middle of it. That will stop water from leaking at the base.

Most MOEN single handle faucets use the same cartridge, the 1200 or 1225. If you have it apart enough to see the top there should only be a few more parts to remove to get at the stem ie the handle and cap. Once there you should see the horse shoe clip that holds the stem in. Once you slide the horse shoe clip off, the stem should be ready to go. Now sometimes these will come out easily, but most of the time they are a little tough. You can use a crescent wrench and gently turn the cartridge at the ears where the horse shoe clip was removed and this will loosen the cartridge, then you can use the handle or what ever you can grab the stem with to pull it out. FYI a lot of the home improvement stores carry a MOEN cartridge puller and they make it a lot easier. After cartridge is removed install new one and your done. DONT forget to turn off water before you begin. Hope this helps.

if we are talking about a faucet then your problem is call the packing nut. sometimes the packing nut cracks or after so many time the faucet been open it just gets wear so what i recommend you to do is turn water off down under the sink and take a screw driver to remove handle, then with a pair of chanalocks remove trim and stem note: make sure stem is in on positiion if not in on position the treats on the faucet may cross treat and then you will have to replace the faucet so dont forget before you star taking it apart turn it off and star removing everything on the top, i will just replace the stem and you problem will be fix. but if you want to try a cheaper solution that may work just remove the handle and the trim and with the chanalocks adjust the packing nut that will be the nut on top of the stem right below the handle and tested.

the whole faucet is bad it has an internal leak replace the whole thing

Turn the water off at the faucet, remove the handle and the retaining nut that is apart of the trim. You will see where you can use a wrench to remove it. The ball assembly will come right out and you can replace the washers right below it. Put it back together and if needed, tighten the tension ring that is on the retaining nut (usually grey or white in color) so it won't leak water around the ball stem. Good luck.