Max Mode increases the suction power of the N79S / SE / W by 50%. This will improve cleaning in especially dirty or challenging environments, but it will also use up the battery a bit quicker.
The only way to access Max Mode is through the app. (You can not enable it via the remote control or on the robot itself.)
First, open the app, and tap the three little dots on the upper right hand corner (See Below)
Then choose "Vacuum Power":
Lastly, choose the "Max" setting, but don't forget to hit Save in the upper right hand corner to confirm the selection.
You will hear the robot shift into a higher gear as the suction increases. To stop Max mode, just repeat the steps, but this time switching it back to Standard.