Lips have a tendency to lose volume with age which is why a lot of people choose to rejuvenate them to make them softer, fuller and perfectly proportioned. Filler products like hyaluronic acid (Juvederm, Restylane, Perlane, etc.) are injected, but they need to be renewed regularly. The filling can also be done by injecting autologous fat (lipofilling).
There is also a surgical option to reduce the size of lips that are too large by making an incision under the nose or the corners of the mouth to reduce the volume of the underlying tissue.