Replacing the fan requires a complete disassembly of the notebook. You will need jewelers screwdrivers, steady hands and lots of patience.
Use the HP Partsurfer to discover which fan/heat sink assembly part number is required for your specific notebook. It is a simpler and very specific method. Once you have the correct part number use Google or Bing to find an online vendor who has the part you need.
Search by using the serial number of your notebook. Use the following link.
http://partsurfer.hp.com/search.aspx
From the Maintenence & Service Guide: ( getting the correct part number is dependent on the configuration of your notebook as seen below)