How to change from showing decks 1 & 2 to 3 & 4?

I have my 2x CDJ 2000NXS' set up as channels 1& 2 playing through a usb, and I have a CDJ850 i want to run through my laptop as channel 3. 

Can I change the 2-deck horizontal view to show decks 3 & 4 rather than only 1 & 2?

I can't find a setting to change it anywhere.

I have tried using all 3 decks through the laptop but it lags like crazy.