You could try looking at disassembly guides for other laptops to give you an idea, but the first time I did it, I just picked up a screwdriver and started unscrewing things! As long as you make a note of where everything goes, it shouldn't be a problem.
Start by turning laptop upside down and removing the battery, and any covers for RAM, HDD etc. to reveal any hidden case screws...
You should be able to find a suitable replacement via the model number of the drive in device manager, or off the physical unit once you get to it.
P.S. a digital camera can be quite useful to take snapshots as you dismantle.
P.P.S. alternatively, get a USB external combo drive; cheaper and generally better quality drives than the internal ones.