To install a bathroom vanity top, turn off the water source to the existing vanity sink, and disconnect the drain and water supply lines. Use a screwdriver to release the clips holding the existing vanity in place, and remove the vanity top. Set the new top into place, center and level it, and secure it with the hardware provided by the manufacturer. Install the new faucet, connect the supply and drain lines, and apply caulk to the sink and vanity.
To level the vanity top, center it on the base, and insert shims between the base and top as needed. Cut the shims off so they are level with the base, using a utility knife before securing the top with the provided hardware. After securing the vanity top, apply a bead of caulk around the joint where the top meets the base, and apply a bead of caulk around the joint between the sink and the vanity top.
Tighten the water supply lines and the locking collar on the drain pipe using an adjustable wrench, but do not overtighten the locking collar, to prevent damaging the sink or pipe. Turn the water on, and check for leaks after the installation is complete.