Changing a circle to an elliptical path is simple
Change the line
document.getElementById("piccy").style.top=90*Math.cos(position)+125+'px';
to
document.getElementById("piccy").style.top=20*Math.cos(position)+125+'px';
In fact we can remove the change in the .top property we can produce a nice bounce effect
Change the line
document.getElementById("piccy").style.top=20*Math.cos(position)+125+'px';
to
document.getElementById("piccy").style.top=125+'px';
Bounce Animation A working example of the bounce animation
Planets A more sophisticated example of the elipse animation.
Exercise
Build a page that bounces a ball off the sides of the screen.
(hint: You may find the screen.width property useful)