What you want is the "HP HDX 18 Entertainment PC - Maintenance and Service Guide"
Detailed instructions are on the HP web site. Go to http://www.hp.com/go/support/
and enter HDX18t. It will ask if yours is the -1000, -1100, or -1200. Mine is the latter, however I only saw the Guide under the -1000.
Click on "Manuals" and you should see the Maintenance and Service Guide. Enjoy!