This will involve the removal of several tiny cross head screws. Use the right tool or you will likely mash up the screw heads and make things really unpleasant for the next guy. A set of miniature screwdrivers can be bought for £5 or so, so don't go whining about not having them.
Remember to keep a note of which screw goes where so that you can put them back in the right places.
With the machine upside-down, the hard disk is buried 'underneath' the optical drive.
So you need to get the optical drive out first. This can be done by removing the "F5" screw which is near the inboard-most edge of the optical drive, and sliding the drive out outboard-wards.
You should then be able to see the hard drive.
To get the hard drive out, remove the four screws at the four corners, then slide the hard drive in its cradle outboard-wards to unplug the connector.
The hard drive is in a cradle, so if you are selling the hard drive or some such, detach the cradle and keep it together with the screws which hold the hard drive to the cradle.
Installation is pretty much the reverse of removal, subject to application of reasonable amounts of common sense. Be sure to put all the screws back.
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