I'm making this tutorial because I've seen that some sites are selling 3d models ripped from games for an high price.
This, other then being illegal (they are selling a model made by another company without their permission) is also immoral, since extracting the model is really simple and they are taking advantage of the users.
Extracting and using the model for your personal use is not prohibited, but not explicitly allowed, so is kind of a gray area.
The common opinion is that if you do not share or profit for the model, you should fall under the 'fair use' case of the copyright law, and so there should be no problem.
The important thing is to NOT sell or share the models you extracted!
To extract the models you need:
1) The Game - Starcraft 2
Normally you should buy the game, but here we are lucky!
In the last few years Blizzard introduced the Introductive Edition License.
In short, you can download the full game, but access only some parts of it; but for us is enough!
You can download the game here: http://us.battle.net/sc2/en/
2) Tool to extract the raw models from the game - CascView
CascView is an essential tool to extract the models from the game, since they are encrypted in a proprietary Blizzard's way.
You can dowload the program from here: http://www.zezula.net/en/casc/main.html
Or you can use the version I attached to this instructable
Blender is the free and open source 3D creation suite, that will allow us to edit the models and export them in a compatible way.
To import the files extracted with CascView you will need a plugin, m3addon.
You can download Blender here: https://www.blender.org/download/ (i'm using version 3.78b, but it should work in any future one)
You can download m3addon here: https://codeload.github.com/flo/m3addon/zip/master... (It download the latest version) or you can use the attached one
Personally I prefer to use tools3d because is just a on-button-fixer that does not require another installed program, so I'm going to explain this using it, but Meshmixer also works really well, if you know how to use it.
You can use tools3d here: https://tools3d.azurewebsites.net/
You can download Meshmixer here: http://www.meshmixer.com/download.html