You can either download the standalone NetDraw installation package, or download the UCINET installation package, which includes NetDraw. The NetDraw 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. 
Alternatively, you could download and install UCINET, which will automatically install NetDraw.
    For information on changes in NetDraw over time, see the versions page.