Extract the models and materials folders inside to your \team fortress 2\tf\ folder, usually located in

C:\Program Files\Steam\steamapps\yoursteamusername\team fortress 2\tf\


Now if the skin does not show up in-game go back to the directory and drag the .vtf files themselves into:

C:\Program Files (x86)\Steam\steamapps\yoursteamusername\team fortress 2\tf\materials\models\weapons\c_items

Enjoy!!