As mentioned previously you can use
C-l to recentre the window on the line containing the cursor (point in emacs terminology). A related command is
move-to-window-line-top-bottom which is bound to the short-cut
M-r. Use this repeatedly to cycle the position of the cursor (point in emacs terminology) between the top, middle and bottom of the window.
In other words,
C-l recentres the window while keeping the point on the same line, while
M-r moves the point without recentring the window.