This is HP Support, and the download page for the Upgrading and Servicing Guide,http://h10025.www1.hp.com/ewfrf/wc/manualCategory?lc=en&dlc=en&cc=us&lang=en&product=1156509&
On this page scroll down to - Upgrading and Serving Guide, and left-click on it.
(Second file listed)
This is a PDF file download. The computer you are using has Adobe Reader on it, which uses PDF files.
After you click on the Upgrading and Servicing Guide, file name, you will Not see anything happening for up to 30 seconds, or so.
Be patient, as the file is downloading in the background.
The Upgrading and Servicing Guide tells you, and shows you, how to open the computer case. (Page 7)
Barring that you are not able to download this PDF file, I will attempt to tell you how to open the computer case. (If you are using a Dial Up network connection, you may be as old as me, before the file downloads)
1) Computer off unplug the power cable FROM the surge protector. (Not shouting)
THEN unplug the power cable from the back of the computer. (Power Supply)
Now unplug all cables connected to the computer.
2) Lay the computer on a towel on top of a table. Keeps the table, and the computer from being scratched.
Lay the computer on it's Right side. (Computer facing you, the right side is to the right. Hey, don't laugh, lol!)
Loosen and remove the three computer cover screws, on the back of the computer's case.
The computer cover that removes is an L shape. It comes down the Left side from the top, and wraps under the bottom.
Looking at the Top/Back of the computer, there is a screw to remove on the Top, of the Left side of the computer case. (Top/Left side corner)
Looking at the Bottom/Back of the computer, there is a screw to remove from the Bottom, of the Left side.
(Bottom/Left side corner)
Looking at the Bottom/Back of the computer, there is a screw to remove from the Bottom, of the Right side.
(Bottom/Right side corner)
After these three screws are removed, the Left side of the computer cover is slid back about 1/2 inch, (1.25cm), and lifted straight up.
BEFORE you reach inside! (Not shouting)
Your body carries STATIC electricity.
Static can fry out, (Short Circuit), the hardware components inside the computer.
TOUCH the metal frame of the open computer case, to relieve your body of Static electricity.
If you get up, walk away, then return, Touch the metal frame again.
Now, do you wish to disassemble this desktop computer completely, or just remove, and replace a few hardware components?
The above Upgrading and Serving Guide from HP Support tells you, and shows you,
1) How to remove, and replace the computer cover
2) How to remove, and replace Ram Memory
3) How to remove, and replace an optical drive.
4) How to remove, and replace a PCI card, that is in a white PCI expansion slot, on the motherboard.
5) How to remove, and replace the CMOS battery
6) How to remove, and replace a Harddrive
Should you need further disassembly guidance, let me know in a comment.