Try changing the frequency rather than the speed. Speed refers to speed of movement (between tiles) but frequency is the speed of the animation.
However, to change the speed via script, try
object.move_speed = x
object.move_frequency = x
where x is the number and object is $game_player or a follower or an event object.
You would also have to add this little script snippet:
Code:
class Game_CharacterBase
attr_accessor :move_speed
attr_accessor :move_frequency
end
OR, instead of all of that, you could use a script in a move route, where you select the player or event, and just make it say @move_speed = x or @move_frequency = x - that way you won't need the script snippet, and you won't need to set a variable to a player or event object. So that's probably the easier way.