Kv

Try to change the current sprite every X frames. I use a counter for this task. Its value is raised by 1 every thime I refresh the screen. So if I update the screen 60 times per second (which means it's running with 60 FPS), I tell my objects which one of their costumes should they wear for the first 10 frames, then the next 10 and so on until their cycle is finished, then I set the counter back to 0.