In the main PBC operating mode, the Switches button changes the functions of the other 10 buttons. What each button does in this mode is shown in the lower right corner of each button's labels. If you look at a picture of the unit, you'll see that buttons 1-4 have a "FN1" through "FN4" label. These are the function switch controls.
So, to edit the function switch state, you press Switches, then press buttons 1-4 to adjust the switch states. Hold the Loops button to store to the current preset. Press the loops button to exit back to the preset mode.
On the main screen, in the upper left, there are four indicators that show the current state of each switch so you can always see the state of the function switches, no matter what mode you're in.