When you adjust the boundaries of a key zone, the surrounding boundaries are automatically adjusted accordingly.
You can change the key zone range in the following ways:
By dragging the "handle(s)" which divides the key zones, you can change the range of the selected key zone.
In the case of having two key zones split in the middle, you could thus change the lower limit for the upper (new) key zone and the upper limit for the original key zone.
By using the "Lowkey" and "Highkey" knobs to set a lower and upper range, respectively.