I am trying to make my hot water last longer in the shower but I do not know what knob I am suppose to turn or which way I'm suppose to turn it... both knobs are white... one is circular and one is a latch? Please someone help.

The cheapest way is to install Low Flow Shower Head. Then you can insulate your pipes and water heater. Next would be installing bigger heater or secondary hot water heater. Ultimate solution is to install tankless hot water heater. This heater will give you endless supply of hot water. In other words - you will never run out of hot water again.

OK, I'm certainly nothing close to a plumber at all, but I've gotten my hot water to last longer simply by turning up the temperature on the water heater. When I moved in here, I kept turning it up until it would last through both dishwashing and typical showers. (I'm supposing that means I'm turning more cold on and less hot on so that the hot is lasting longer.)

The water heater should have a temperature knob on it. It might not have degrees - mine only has like low, med, high and everything in between, and a red area that claims that's the most energy efficient. (The last time I had one with temperature, I had it at something like 120-degrees, but that was for just me, and I didn't have a dishwasher which really wants to be higher.)

(And when I put in a low flow shower head, my hot water ran out faster.)