The Liquify tool (Filter > Liquify) is one of the more powerful controls in Photoshop. It allows you to push around the pixels; stretch out certain areas, shrink others, pull in a jawline, any number of things. It’s the “airbrushing” side of photoshop. The panel on the left of the Liquify window actually dictate what your brush is going to do; holding your pointer over them reveals the tooltip descriptions of each. The topmost, Forward Warp, is probably the most useful as it nudges the pixels in the direction you push the pointer. To adjust intensity and amount of movement, change your brush size and density, respectively.