An excellent write-up explaining how the ISS avoids space debris with mention on how thrust is provided by the Zvezda Service Module engines or, when docked, by Progress vessels or ATV. Via Lee Hutchinson at Ars Technica.
Additionally, the station has several sets of thrusters that allow it to rotate and translate. The Zvezda service module is equipped with thrusters, and there are thrusters on docked vehicles like the Progress resupply craft and the ESA ATV that can also be employed. For a typical debris avoidance maneuver, the station will be subjected to delta V of between 0.5 and 1 meter per second.