How do you keep the ISS stable in orbit?

15 year-old George Kristiansen from Upton in England received a video from ISS Astronaut Frank De Winne ON1DWN in response to his question.

Watch George ask "How are minor modifications to the ISS's orbital trajectory and altitudes made, in order to keep it in a stable orbit?"

Watch the reply from Astronaut Frank De Winne ON1DWN