Remove the old counter top. Stone or cultured marble are usually just laid on top. A bead of caulk around the frame inside the cabinet keeps them in place. Using a razor-knife, cut through the caulk around and underneath the old countertop. Laminate, tile and wood countertops are usually attached by being screwed from underneath.
Lay the new countertop in position and caulk around the underside as necessary to keep it from shifting. If you have a separate lip around the top, caulk the backside and press to the wall.
Caulk around the counter top edge. For clean lines, use painters tape to mask off any areas where you don't want the caulk to go.
Install faucet and hook up plumbing.
Types of Countertops and Design Decisions:
Countertop Material- Cultured Marble is generally the cheapest, but there are several price grades depending on which type of marble you select. It's very similar to the way kitchen countertops are rated A,B,C,D. Each letter has a different price point.
Matte or Gloss Finish - Matte finish generally costs around $50 more.
Type of sink - Integral (made of the same material as the counter), or Non-integral (they mount a porcelain sink to the underside of the countertop). There is an upcharge for the non-integral, but it's more durable and harder to scratch in my opinion.
Sink Bowl Shape - square, rectangle, or round.
Backsplash lip - You can choose between an attached 4-inch lip (pictured in the before photos) or an unattached one (pictured in the after photos). The choice is yours, but if you have walls that aren't parallel with the vanity top, I would recommend an unattached lip. You can hide that flaw much easier. If you're planning to add tile around the vanity, skip the backsplash lip entirely.
Other customizations - Sometimes, you have the option to choose a specific edge or thicker front to simulate granite.