I took a shower today and the hot water turned to cold in only 2 or 3 minutes. I'm assuming that the water heater needs to be adjusted. I want to know how to do that or what else could be causing the water to go cold faster?

Unless the power was off, the only way it would get cold that fast is if the dip tube is broken off. With a broken dip tube, the cold water coming in stays on top as it short circuits to the hot side. Dip tubes can be replaced but you would have to disassemble the cold water input side to check.

I am no plumbing afficianado but my sister had that same problem just last week and it turned out to be the pressure relief valve. She could hear water running out the overflow continuously but it took them a while to find the problem. For what it's worth.

You could also have a bad bottom element. You need to check it with a meter first to make sure that an element has not burned in two. Turn off power and remove one wire on each element and check the elements on "ohms."