I have no experience myself with replacing the belt on this compressor.
Maybe another visitor can comment on this answer with their experience?
But, you can find the parts lists of this compressor here: http://www.homedepot.com/catalog/pdfImages/62/621248d7-b317-4167-b3de-f0c3995e0067.pdf?cm_mmc=seo|altruik|100653165
You can see the belt on page 5. There doesn’t seem to be any tension adjustment mechanism, so it’s just a matter of opening it up, removing the belt and putting on the new one.