You should replace the propellers if any one of them is scuffed, marked, scratched, bent, or damaged in any way. What might look like nothing more than cosmetic damage can upset the aerodynamic balance of your drone.
Here’s how: Each blade is marked on the top to show the direction in which it spins. Each motor has two blades and one set of two circular flanges with two screws that hold the blades in position. Use the included Allen wrench / hex key to loosen both screws on the motor and pull each blade down from its circular flange and then straight out, away from the flange.
Replace with blades that spin in the same direction. Please fasten the replacements tightly. We recommend replacing all eight propellers and four flange sets together to ensure maximum efficiency, and more stable flight.