The Warp command in Photoshop is fantastic for reshaping layers into any form you like. To initiate it, go to Edit > Transform > Warp (or, instead, right-click while transforming a layer to access the Warp feature). There are a few crucial controls. First, the grid in the top-left lets you set how many segments your warp box has. The more segments, the tighter the changes you can make. As well as choosing from a standard grid like 3x3, you can also Cmd/Ctrl-click to add your own anchor points on the layer. Now you can either drag a single point; or hold Shift and drag a box to highlight several anchor points, then move them all at once. If you’re after more pixel-pushing controls, head to the Liquify command (Filter…