If your water has NO hot water, then click circuit breaker
Next, click red reset button.
Turn off power.
Open cover on water heater.
If heater has 2 covers, open top cover
After re-seting water heater, insulation must be put back over thermostat to prevent cooler air from affecting thermostat.1) Reset button is a good starting place to check water heater
Reset clicks off for a number of reasons, including overheated water.2) Reset will not reset
, then replace thermostat.http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html3) Resets clicks on, but clicks off again later
, you should diagnose the problem.
Clicking reset is not a hazard
Click the reset as often as you want until you have time to diagnose.http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html4) Reset is not tripped, and you still do not have hot water
Then use tester on top two screws (T1 - T3 screws -or- 1 and 3 screws) of upper thermostat to check if you have power.
If you have power, then replace thermostat.
If problems continue, a full diagnosis is needed as per the link above
If you need more help, add a comment and I will respond