Go to "support.dell.com" and enter the service tag number - OR enter the model number and follow the prompts. Then you can download the Service Manual and proceed from there.
I would suggest that you take some digital pictures of the existing setup before you start disconnecting stuff. And keep taking pics as you disconnect. This is what I did with my Dell Precision WS 490 when I added a drive, and did some modifications. Also, mine was purchased used, and the insides were covered in oil. I took out the fans and cleaned them with solvent, and did the same to the interior.
^1 good advice Ubrales
Harry it is easier than you would think.
One piece of advice is buy heat sink compound Artic Silver and clean off heat sink of old and use new compound (about a pea sized dot in middle)
when you put in the cpu(s) match up the triangle in corner of chip with socket and let it kinda slide and drop in.When it is in place it should sink just a little.Then gently push down
I dont like using the latch because you lose your sense of feel and can bend a pin
If you do bend a pin sometimes you can carefully bend it back but lets hope that doesnt happen
When putting back together double check all power leads are in and front panel plug is in.
First time I did it i didnt put in front panel switch plug in and freaked out when it wouldnt turn on LOL.
Make sure Heatsinks lock down tight.