You at least need to give that number a unit, like 0.5 pixels, 0.5 tiles, 0.5 screens, ... assuming you mean tiles, I suppose you mean 16 pixels then. If so, search for the following line in Sprite_Character:
self.y = @character.screen_y
Change it to this:
self.y = @character.screen_y - 16
If I got your request wrong, you should be able to change this by yourself now, as it's pretty simple to play around with...