How do I edit the number of beams in a measure?

This feature is available to users of FORTE Home and FORTE Premium. You'll need to redefine the meter manually. In a general 4/4 meter, 4 eighths are beamed together.
If you would like for only 2 eighths to be beamed together, you'll have to change the meter to 2+2+2+2/8:

Press "ctrl+1".
Double click on the time signature.
A window, "Meter Properties", opens.
In the upper part of the window, you can define the meter manually.
Subsequently, in the lower part of the window, you can decide how your meter shall be displayed.
Confirm you selection by clicking on "Apply".