Scratch

hey, i got this assignment, to make a game, i made a game, pretty simple. doding the falling thing. very simple. i got it all programmed out to fall, and re-appear and stuff. and whenever a rock hits the bottom, you get a point, i made a score using a variable. or whatever.
anyway i problem is this. i need to make it challenging so after the score gets to 30. i want the speed to increase, and if you get hit the speed decreases, and so on. is there anyway to program to set the speed to a certain level? like a speed lvl of 1 which goes fast, and a lvl 2 which goes faster, and lvl 0 which is original speed. cuase right now i got it programmed that it moves steps faster, and its not working well. so please help me. i can upload my game if that helps.
thanks.