How do you switch out the single lever dial on a delta shower fau

http://www.deltafaucet.com/parts/id-my-product/index.html?reset=true#wiz you should be able to track down the one you have on this "troubleshoot your product
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can be a number of issues: clogged aerator, water supply is turned off, or supply lines are kinked, debris behind cartridge blocking flow, rubber seats out of place.... What has changed to cause problems?

If you have the type that you turn the handle like a clock, you have to find that perfect spot. It can be 3/4 of the way around. If you have the ball type, single lever, the rubber seats and springs under the ball should be replaced. Cost...less than $10 for the kit to do yourself.

pull off temp. cap see the handle screw

It sounds like there's a blockage in the valve. It needs to be removed to see if water is blocked and confirm you have hot flowing freely.

If you replaced the seats and springs and the problem continued you may need to get a whole rebuild kit including the ball and replace that one as well

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.

Is there a button on the tub filler? How about the spout on the tub, does it lift up? If there is not a tub spout then it should be shower only, if it has a tub spout it has to have a lifter of some sort, the foto I found showed the little button lifter. Hope this helps.

It takes a 1/8" allen wrench to remove handle. To increase hot water flow remove plastic dial that sets temperature. It is right behind handle and slides off stem for easy adjustment.

Remove indicator and replace about 1/8 to 1/4 turn counter clock wise to increase to hotter temperature.

Some of the new units have stops installed on the valve itself. Make sure they are open.