Turn off the bathroom light and set up your stepladder or chair underneath the panel that needs to be replaced. Climb the stepladder or stand on top of the chair so you can reach the panel.
Lift up on one side of the panel and pull it on top of the adjacent panel. As soon as the far side of the panel clears the support, tilt it slightly sideways so the sides clear their supports, and then lower the entire panel down to the floor.
Pick up the new panel and insert one side into the suspended/dropped ceiling area. Push it in far enough for the other side to clear the panel support. Set it inside the panel supports, climb down, and then turn on the light to see how your new panel looks.