Mac Startup Security Utility - switching from Medium Security to Full Security

In Mac Startup Security Utility there are three different levels of Secure Boot: Full, Medium, and None (No Security).

Switching from Medium to Full is a bit confusing. 

Here are the steps:

1. The computer must be on your network, either with Ethernet, or by connecting to wifi.  The wifi icon is in the upper right of the screen in the menu bar.  Select your wifi network and enter the password (because you're in Recovery Mode, the Mac doesn't have access to your wifi password from your boot drive).
2. Click the radio button to change Medium Security to Full Security.
3. It will ask you to select a startup drive, and bring up the startup drive selection application.  Once you select the drive, you must click the Restart... button in the lower right of the window.  If you just exit startup drive selection it won't work.

Once you have restarted, you will be back in Full Security mode.