With the photo open in Photoshop, duplicate the layer (Duplicate layer) and then click on Filter menu and select Liquify to open the filter allowing to modify the shape of the object in all possible ways.
On the control panel in the left part of the window file select Forward warp tool and distort the surface and compressing it, and choose a suitable brush size and its density and pressure, depending on what part of the body will decrease. Size during editing, you'll be adjusting constantly, because different body need different size brushes.
In order to prevent distortion of those places that you want to leave unchanged, treat them with the Freeze mask tool.
Treat the desired area of the figure by a filter and click OK to apply the changes to your photo. To make the change realistic and get rid of blur and fuzziness on the treated areas, again, open the filter menu and select Sharpen.
Then set the transparency level of the layer (Opacity) to 50% and create a layer mask Create layer mask). After that, invert the mask by pressing Ctrl+I.
Selecting white color on the palette, paint brush distorted at the beginning of the treatment region, and then slightly reduce the transparency of the layer. The photo's sharpness will return, and the changes will look good.