Both fans in my 15" Macbook Pro A1226 (2007) were making lots of noise.
Once you get all of the screws out holding the case on, the top with the keyboard pops right off and there are the fans. I carefully unplugged the fan connections and used a T6 screwdriver to remove the screws. When pulling the old ones out, you must be careful about the other wires/connections in the vicinity, some of which run across the fan. With the old fans out, I popped in the new ones, screwed them back in and plugged in the connections. Like new!
Make sure you get the two screws inside the battery compartment that are under the touchpad and check to make sure you've gotten every screw before resorting to a spudger.
TR6 Torx Security Screwdriver
MacBook Pro 15" (Model A1211, A1226, and A1260) Left Fan
MacBook Pro 15" (Model A1211, A1226, and A1260) Right Fan