Toilet Tank not Emptying

My toilet tank is not emptying. This is causing the flapper to not fully close as there is too much water in the tank for it to go back into place fully. What and where is the adjustment to ensure all the water in the tank is used in the flushing process?

Any help greatly appreciated.

TRM

Most newer toilets do NOT let all of the water out of the tank during a normal flush cycle. They use the height of the water to provide more "head" or pressure to do a good flush. But, if the toilet is not a decent design, it won't matter much anyways.

put a fluidmaster flapper on it.......

If it's a relatively new toilet you might go online and search the manufacturer's website for info - I was able to do this for my 2yr old Kohler toilet - I found and printed out the installation instructions and spec sheet, which helped us to figure out how to adjust the stuff in the tank.