I believe the default gateway for Westell is 192.168.1.1. type this address into your browser and hit enter.
This should bring up your routers web interface, you may or maynot be prompted or username and password. Try admin/admin or admin/blank (empty for password)
Once you login there should be a wireless or secuirty tab that allows you to setup secuirty.
NOTE: Look
HERE for info on wireless secuirty DO's and DONT's