First, 
Download this design from Thingiverse.
                  Next, you will need to import the design into a Computer-Aided Design (CAD) program. We recommend 
TinkerCAD, a free online app made for anyone of any age to modify 3D printable designs.
                  In TinkerCAD you can quickly change the size, add text, remove parts, or combine with other designs. Learn more about 
remixing in TinkerCAD here, or more generally about designing 
here.