Search the disk for tar.exe and note the directory it resides in.
Then modify the system variable path to include this directory at the end.
Control Panel>System Properties>Advanced System Settings link>Advanced tab>Environment Variables button>Scroll down the System Variables section to find Path and click edit and then move the cursor to the end of the line and add a ';' and the directory from above.
Then click o.k. and exit the control panel.
Then go to the directory $NH_HOME/upgrade and double click on installOneClickEH.sh.