The visible note range in a MIDI track can be controlled in two principle ways: the note scroomer, or the scroll wheel of your mouse.
The scroomer offers two kinds of control. You can "grab" it in the middle and move it up or down - this adjusts the absolute note range displayed up or down. Alternatively you can "grab" the top or bottom handle of the scroomer, and move that up or down - this adjusts the extent of the note range displayed.
Several scroll operations can be used to control the visible note range: