Remove the bathroom vanity by unscrewing the screws from the wall, being careful to support the vanity during the removal process. Set the screws aside in a secure place to be used for the reinstallation.
Reposition the vanity slightly higher on the wall so that the holes are lined up with the same studs as the previous installation. Support the vanity in the desired position with the help of an assistant. Set a carpentry level on top of the vanity and adjust the vanity until the level reads that the vanity is straight. Mark the position of the holes in their new positions. Set the vanity on the ground away from the wall.
Drill holes into the markings in the wall using a drill bit that is slightly smaller in diameter than the installation screws, hitting the studs with every hole to ensure stability. Redrill any holes that do not find a wall stud. Reposition the vanity with the holes in the vanity over the holes in the wall. Set the original installation screws into the holes and tighten them halfway. After all the screws are tightened halfway, tighten the screws completely to attach the vanity to the wall.