Depending on the year of manufacture, the attachment points may differ.
Front bumper
-open the hood.
-under the hood, Unscrew the four screws and remove the grille up.
-under the grille take out three pistons (inserted from top to bottom).
-on the perimeter of the lower part of the bumper, Unscrew the four screws and take out the four pistons (twisted and inserted from the bottom up).
-in the lower grille, Unscrew the two screws.
-turn the wheels to the side.
-in the wheel wells take out the caps that secure the fender liner (front) and Unscrew the screws that secure the corners of the bumper.
-we release the latch in the wings (pull the corners of the bumper towards you).
-with an assistant, pull the bumper forward (look for the wires).
-disconnect electrical connectors.
Rear bumper
-open the trunk lid.
-unscrew two screws on each side and remove the rear lights (held by latches).
-in the opening of the trunk, Unscrew the four screws.
-in the side trims, Unscrew two screws on each side and remove the trunk lid guides.
-remove the lining of the rear trunk panel.
-behind the casing, through the holes, Unscrew the two nuts.
-around the perimeter of the lower part of the bumper take out the caps.
-in the wheel wells, Unscrew one screw on each side that attach the corners of the bumper to the wings.
-we release the latches in the wings and under the taillights (blue arrows, pull the corners of the bumper and the sides of the lining towards you).
-with an assistant, pull the bumper back (look for the wires).
-disconnect electrical connectors (if any).
How to remove the front and rear bumper Toyota Alphard (2008-2015)
How to remove the front and rear bumper Toyota Alphard (2015+)