On a vehicle with a serpentine belt system there is always a tensioner pulley. Usually in the center of the routing network, you need to place the correct size wrench on it and push or pull with one hand releasing the tension on the belt. With the tension released, use the other hand and slip the belt out.

Most vehicles have a sticker in the engine compartment for replacing the belt to be sure it is put back in correctly. If not, be sure you look at the routing and or draw a picture so that it is replaced the same