I instslled new delta single shower faucet ,the water is running for 5 to 10 sec even if the shower handle is in off position

Take the handle off and adjust the hot temperature stop. Its just a plastic piece that needs to be adjusted up more. It just fits in grooves like a gear. Its easy to do.

change the cartridge

easy way is to install a shutoff valve on the shower head.

Hidden under the lever is a little hex screw. Use an appropriate hex a.k.a. "Allen" wrench to remove the handle. You might want to shut down the water service first to save your shower until later.

REPLACE THE CARTRIDGE. TURN OFF WATER, REMOVE HANDLE AND FACE PLATE. REMOVE TWO SCREWS UNDER PLATE. PULL OUT CARTRIDGE AND INSERT NEW. REASSEMBLE

If you are handy, the best solution is to call delta and have them send you a new diverter. They will need the model of your faucet. The new diverter will come with instructions on the install process. As far as fixing it without the new diverter, I don't believe you will be able to.

bad faucet...get new at lowes or home depot

You might have to replace the tub spout, because the divirter is not closing all the way. A new one will stop water from getting by it.

I have to assume you've unscrewed the face plate, not removed it, because you can't do that without taking the handle off. Delta handle usually come off by unscrewing an allen (set) screw just under the handle itself. Sometimes these are covered by a plastic plug.

Occasionally, even after you've completely removed the set screw, the handle still won't come off. Wiggling and pulling for a few minutes will generally get it off. If not, then a hacksaw, new handle and new cartridge are the answer.

If the allen screw is stripped and that's why it won't ome off, see above.

Good Luck.

you have to take the handle off
there should be an insert that you can adjust by pulling out and turning