Changing your pully isnt going to change anything if you have the out of date tensoner. The upto date tensoners have a small hdryaulic piston instead of a spring.
If you need to change it do the same thing as barney told you to do but you will also need a 13mm and a 10mm socket. Theres 3 10's and 1 13mm that holds the pully on.
The new tensoner comes complete with pully and all the hardware your need to assemble it. There is 1 trick putting the tensoner together, you have to compress the piston with a pair of large plyers or a vice. You cant do it with your hand so dont even waste your time. The job is sliglthy complex, if your more hands on Im sure you can find a how-to on line somewhere. If you dont know how to open your hood, it might be a good idea to take it to the dealer.