When you get the proper socket try turning it easily with the socket and see if the tensioner pulley starts moving to allow loosening the belt. If it does then keep turning it till it won't move anymore. That is how the ones I am familiar with work. The tensioner pulley bracket is spring loaded. If the pulley does not start moving then yours is different and you will have to get an answer from someone that is more familiar with this model. Should be pretty straight forward on which direction it should turn based on the way the belt wraps around it.