The Stretch tool is often used for distal lengthening/shortening (for prosthetics) or for adjusting the angle of a foot after taking a scan for an AFO or other orthotic. It's an incredibly powerful tools with a variety of uses!

First, use the Select Region tool to define your region. 

Next, select the Stretch tool. You can use the Set Centerpoint to click set the center of rotation of the stretch. 

You can use the arrows and curves to move the shape manually. Another option, is to  enter a quantitative value and direction in the box. Click Move to perform the action.