To remove a tensioner pulley, you need a flat bar, such as a crowbar or screwdriver, and an adjustable wrench. You can remove a damaged pulley quite easily.
Refer to your car manual to locate the belt tensioner and pulley. It is difficult to access the drive belt in some vehicles, and you might need to remove a wheel and a splashguard to access the belt tensioner.
Insert the flat bar between the tension bar and the tension pulley. The point of the flat bar should point towards the tension belt. Ensure the flat bar is in contact with the tension pulley and the tension bar by raising the handle of the flat bar. Create a slack on the tension belt by forcibly lifting the flat bar to rotate the tension pulley on its axis.
Slip the belt off the engine head through the easiest accessible pulley. Do not remove the belt entirely unless you are replacing it. Allow it to lie free to eliminate excessive tautness.
Locate the nut that secures the tension pulley, as it may be hidden beneath the pulley. Loosen the nut by turning it counter-clockwise until it is completely free. Carefully slide the tensioner pulley off its axle.