Changing the filter in a reverse osmosis system involves replacing the old filter cartridge with a new one. Identify the filter housing unit, typically located under the sink or in a cabinet. Shut off the water supply and release any remaining pressure in the system. Unscrew the filter housing, remove the old filter, and insert the new one. Tighten the housing back in place, restore water supply, and flush the system for a few minutes to remove any residual particles. Refer to the system’s manual for specific instructions and safety precautions.