In the event that boost is on, the screen will display a "B" as in the middle image below. This will be displayed no matter which mode is selected, but will only be run in automatic.

Press the info key (key 7). You are now in the main menu, and the screen will be the same as the image below.

Press the right arrow key (key 5). In the event that boost was off, the screen will be the same as the image below. If you are turning boost off, then "Now:" will be "On", and "Set:" will be "Off".

Pressing the up arrow key (key 4), will toggle the "Set:" parameter. i.e. If like the image above it is reading "On", pressing the up arrow key will set it to "Off". When you have the desired setting press the enter key (key 8), and the setting will be accepted, and you will be returned to the main menu.
If you have changed your mind, pressing the left arrow key (key 3), will return you to the main menu without changing the boost setting.

You can now press the left arrow key again to return to the default screen, or press the up, or down arrow keys to select a different menu item.