Hello everyone,
First of all, sorry if I'm going to make mistakes or for my bad english, enjoy it.

Step 1: Download

First of all, download WoWModelViewer below:

WoWModelViewer - 32bits
WowModelViewer - 64bits

Choose your windows and install it.
(If you meet some problems during installation, please tell me it)

Step 2: WoWModelViewer

Open it, You'll get a window in the middle

Select "Yes"

After doing it, select "Character -> (the race that you want)" I'll take human female.

You can edit skin, eyes, face with the right window.

Now, we'll gear it. (If you have no idea about the gear, go on wowhead)
There is two ways to equip it, first way, you can take the item ID from wowhead and put it:

Like: http://www.wowhead.com/item= 35033 /brutal-gladiators-leather-helm

And then, copy and paste in wowhead

second way is than you only have to write the set name, like it:

now done on the entire character.