Level select:

Press Up, Down, Left, Right at the title screen. A number that
corresponds to the starting level will appear on the top right
corner to confirm correct code entry. Press Up or Down to select a
level.

Super jumps:

Approach a jump at 200 kph and press Down, Up at the top of the
jump. The speed of your bike will remain at 200 kph. Then, press 1
while in the air, and press 2 just before your bike hits the ground.
This will allow your bike to remain in the air for a longer amount
of time.