Replacing a bathroom light fixture is straightforward and most homeowners can complete it in under an hour. Kill the power at the breaker first — not just the wall switch.
Kill the breaker. Verify with a non-contact tester. Remove the canopy, disconnect wire nuts, and take down the old mounting bracket.
Attach the new bracket to the electrical box. Connect black to black, white to white, ground to ground. Secure with wire nuts and give each a firm tug.
Tuck wires into the box. Secure the canopy. Install bulbs. Restore power and test.
If you find more than three wires in the box, aluminum wiring, or any signs of burning or melting, stop and call a licensed electrician.