This was not my guide, i have just posted it on here to share with the community.
Enjoy.
--
First: Download MyWarCraftStudio at http://vy.is.noodley.com/MyWarCraftStudio_0.10.6337.rar
Second: Open MyWarCraftStudio, go to File > Open > C:\Program Files\World Of Warcraft\Data\Common.mpq
Third: Expand the CHARACTER(WITH CAPS) tree, make sure you have All file(*) selected. Now go to folder of the race THAT YOU WANT TO BE for example Human Male. Expand the Human folder, then the male folder right click HumanMale.m2 > extract file to desktop.
Fourth: Rename the HumanMale.m2 to the race you are currently. So for example if I want to change my Undead male to Human Male, rename the HumanMale to ScourgeMale.m2
Fifth: Make a folder on your desktop called 'CHARACTER' in CAPS in that folder create a folder with your current race, so for me Scourge. In the Scourge folder create a folder with your gender, so for me Male. Now you should have CHARACTER\Scourge\Male, copy the ScourgeMale.m2(HumanMale.m2) into the Male folder.
Sixth: Go to Pack> Create MPQ Archive and save it as patch-3.mpq on your desktop.
Seventh: Now right click in the white area(beneath C:\Documents.. yada yada) and select Import folder.
NOW TYPE, TYPE TYPE TYPE CHARACTER in the white box and press enter twice. DO NOT MOUSECLICK OR IT WONT WORK!
Eighth: Save and close Archive, delete the CHARACTER folder from your desktop( DO IT! )
K SO NOW HUR COMES PATCH-4.MPQ
First:Open MWC> File > Open > common.mpq
Second: Expand the Character tree(without caps!) and go to the folder of the race that you want to be, for example human. Right click the human folder > Extract folder > Desktop
Third: Rename the folder to what race you are at the moment, Scourge(SCOURGE seeing its case-sensitive and blizzard did SCOURGE and GAYELF in caps) for me. Delete the folder of the gender that you don't want to change(Female in my case)
Fourth: Download XNview(http://perso.orange.fr/pierre.g/xnview/endownload.html) install it and open it.
Fifth: Go to your desktop IN Xnview, press the folder of your current race(SCOURGE) for me and click on the Male folder. Select all files(Ctrl+a) and press F2. Click the Replace thingy and enter the name of the race/gender that you want to be(Note: ITS CASE-****ING-SENSITIVE) so HumanMale for me. At the With bar you type the race/gender that you currently are so SCOURGEMale for me. Now press Rename.
Sixth: Create a Character folder on your desktop(This time without all the caps) and place the folder of your race in it(SCOURGE for me)
Seventh: Go to pack > Create MPQ archive and save it as patch-4 on your desktop.
Eighth: Now rightclick the White Area and press Import folder. Now type, TYPE TYPE ****ING TYPE Character in the white box and press enter twice.(IF YOU MOUSECLICK AND WHINE TO ME ILL ****ING MURDER YOU)
NINETHHEHEHT: Pack > Save and close archive
NOW PUT THE PATCH-3.MPQ and PATCH-4.MPQ IN YOUR DATA FOLDER.
Now download http://vy.is.noodley.com/ModelChange210.rar, unzip it PLZ and place it in your WoW folder. Open WoW with it instead of your WoW.exe otherwise the modelchanging won't work