Install the new mounting bracket that came with your fixture (if you bought a used one, you may have to use the old mounting bracket from the Hollywood Strip).
Attach the screws through the bracket and into the junction box.
Once the bracket is level and fits snugly with only a small portion of the headless screws poking through; remove the light fixture and tighten the screw in the middle of the mounting bracket to secure the rotating bar.
Wrap the ground wire from the junction box around the green or bare screw on the mounting bracket.
Twist the black wires from the junction box and the light fixture together. Repeat the same process to connect the white wires.
Gently fold and tuck the wires back into the junction box.
Once the light is separated from the base, check all wires for voltage.
If all is safe, remove one wire nut at a time, separate the wires and screw the wire nut back on the wall side.
There may also be small screws on the sides of the light holding it to the mounting plate.
Locate any other screws that might be holding the fixture in place. Remove the mounting bracket……and now you should be able to remove the light fixture.