STEP 1 - Make sure you have GiD installed. The DEMPack Team always uses the latest Developer version of GiD. If you wish to install it now, you can obtain it from GiD's Download page
STEP 2 - Download the D-DEMPack package that fits the most your Operating System (Windows 32 bits, Windows 64 bits, Linux 64 bits) from the DEMPack Website (label 'Software').
STEP 3 - Extract the content of the downloaded package and copy it into the Problemtypes folder in the GiD installation folder.