How do I change the number of helpers needed?

The number of helpers can be changed only at task level. 

(An activity simply displays the sum of all helpers on tasks within it. so to changer the total helpers on a stall or activity, you need to change the min and max values on the tasks within that activity.)

So to edit the min and max values, just click on the number of helpers in the task, then you must PRESS ENTER on your your keyboard to save the change (IMPORTANT), or it reverts back to the original settings. Watch this super-short video below.

N.B. Make sure you do not try to set the minimum number greater than maximum or you'll, or the maximum to be less than the minimum or you'll just get a message saying "something went wrong"!