The temperature on a water heater can be adjusted to the temperature of your choice. The issue becomes what temperature to set it at. The setting for a dishwasher to properly clean the dishes is higher than you want the the temperature for showering. You may need to adjust the heater a few times to get it to the temperature you are comfortable with.
There are codes that specify the requirements for professionals to set a water heater at. As the home owner you are free to set it where you would like. Just be aware that setting it too high can cause someone to be scolded by the hot water.
Each unit is a little different in were the controls are to set the temperature.
A standard tank gas water heater will have the temperature control knob on the gas valve on the front of the unit. It will be a big turn knob.
An electric tank water heater temperature control will be inside a cover that is screwed to the side of the heater. You will need to remove the cover to access the heating element and thermostat.
On-demand units, also know as tankless water heaters, will have temperature control buttons on the front of the unit. Most will have a digital display showing what the temperature is set at.
Setting a water heater to the correct temperature is important so you don’t get burned by water that is too hot. But if it is too cold, it could grow bacteria.