To  increase  your  altitude BEFORE you've taken off, press Y then F4.
When you want to stop going up, press Y again. Anytime during the game
press  "y".  You  will stop and so will everything. On the top it will
say "slew" Then press either F2 to go forward o r back and F1 to stop.
Or  press  F4  to  go  up  or downand F3 to stop. Also when you are in
"slew"  mode  you  can  the can go forward, back, right left using the
arrow  keys  on  the keyboard or the joystick. When you are done press
"y" again.