In order to increase Fmax, you must 'crop" the collected image. The best way is to decrease the vertical resolution (Height) of the image which allows you to increase the acquisition rate. Decreasing the Width of the recording will also allow you to increase Fmax, but at a slower rate.
See the video below for exactly how to do this and just what it means.
What is the difference between a Region of Interest (ROI) and Zooming the View?