How can I adjust the temperature of my hot water?
There should (might actually) be a thermostat control on the water heater unit. Typically, in the US at least and on the units of which I've experienced, it's a big, round, red knob which will give you suggestions like "HOT", etc. Today's more efficient units may even have an "Energy Efficient" specific setting.

Adjust it to your liking.

Note that this may not be a feature on all models, particularly an electric heater; I know mine doesn't.