Its simple. You just need SSH access on your server with root access.
Nginx Admin Install instruction:
cd /usr/local/src
wget http://nginxcp.com/latest/nginxadmin.tar
tar xf nginxadmin.tar
cd publicnginx
./nginxinstaller install
To update or Unistall Nginx Admin you need to do the following
cd /usr/local/src
wget http://nginxcp.com/latest/nginxadmin.tar
tar xf nginxadmin.tar
cd publicnginx
./nginxinstaller uninstall
If you are upgrading versions, just install it again.