go into game_player and find this line
def update
it is around line #204
you should see this code below that line.
case Input.dir4
when 2
move_down
when 4
move_left
when 6
move_right
when 8
move_up
end
replace that block with the following
case Input.dir4
when 2
move_down
when 4
move_left
when 6
move_right
when 8
move_up
when 7
move_upper_left
when 9
move_upper_right
when 3
move_lower_right
when 1
move_lower_left
end
and finally,you have 8 direction movement