The first thing you need to do after you have a plan is to start taking down the old fixtures and components. If there is a mirror, tackle it first, but be careful because if it's glued on, the job can be a little tricky. Begin by running a 5-in-1 tool along the edge of the mirror. If the room has been painted since the mirror was installed, the dry paint could make it more difficult to come off. By using a flat pry bar, start at one end, carefully start prying the top edge of the mirror, making sure not to apply too much pressure. Move along the top edge and simply pull the mirror loose in small amounts.
Note: In addition to the brackets that hold the mirror, it may also be attached with mirror mastic. You must be extremely careful removing a glued-on mirror to avoid breaking the glass.
Once the mirror is off, it's time to remove the vanity and the lights. First, remove the bracket(s) that were used to hold the mirror in place.
Begin the task of unhooking the connections under the vanity:
Now the vanity is free to be lifted and removed from the base cabinet.
Next, remove the baseboards along the wall. This will make it easier to remove the old cabinet.
Remove the P-trap portion of the drain.
Whenever you have to disconnect the P-trap portion of the drain or any other drain assembly, it's a good time to clean it out and inspect any seals or gaskets that can develop a leak in the future. Replace any that have significant wear and tear.
Turn off the water-main valve and remove all of the shut-off valves. This will let the pipes slip through the holes.
Remove the screws that hold the cabinet in place and remove the base cabinet from the wall.