You can either download the complete installation package or just the exe. The installation package will uninstall any old version you have (but keep your data files), install the new one, and add it to your Start menu. The exe is just the exe. You could replace your old netdraw.exe with it, or just download it somewhere else and double click on it to run it. (Note that if you do this, and you want to run netdraw from ucinet, you will have to tell ucinet where to find netdraw. In ucinet, go to options|helper programs.)
Alternatively, you could download and install UCINET, which will automatically install NetDraw.
    For information on changes in NetDraw over time, see the versions page.