Turn off power to the water heater at the breaker
Remove the access panels and insulation
Verify power is off with a non-contact voltage tester
Disconnect the wires from the heating element terminals
Set a multimeter to continuity or ohms
Place one probe on each element terminal
Read the resistance value
Check for continuity between each terminal and the metal tank
Replace the element if there is no continuity across the terminals
Replace the element if there is continuity between a terminal and the tank
Reconnect the wires
Reinstall insulation and access panels
Restore power to the water heater