Hi,
Here is a link to the [http://www.hp.com/ctg/Manual/c00481822.pdf|service manual] for your laptop.
Scroll to Sect 5-70 to view the necessary pre-requisites and then the procedure to remove the fan assembly.
The fan assembly is included in the heat sink assembly spare part kit, spare part number ''384622-001''
Here is a link to [https://www.ebay.com/p/HP-Pavilion-Dv4000-Cooling-Heatsink-and-Fan-384622-001/1900238782|suppliers] of the spare part. It is not a recommendation to use them, it is shown just to give an idea of the price. There are others online that may suit you better. Just type 384622-001 in the search box to get results.
Hopefully this is of some help.