The online guide is here:
I would go to (page 2-5 of the manual above) first and run a Hard Drive test from the Tools menu, before replacing.
Then go to replacement procedures (Page 5-7 of the manual) and it will instruct you, it is very simple, usually taking out two screws, removing the caddy (plastic holder). You then unscrew the old hard drive from the caddy (four screws) and then screw in the new hard drive (four again), slide it in, screw the caddy in (two screws) and voila', your new hard drive is installed.
This does NOT include instructions on how to backup your files, re-install your software or anything OTHER than replacing the physical hard drive.
You will need to format the new drive and install an operating system and software.
If you need further instructions, please ask.