Download the skin and import everything you got from the zip to your map.
The main model (.mdx) should have its path NOT changed.
You should have also got 3 skins.
HeroTinkerTank.blp uses this path > units\Creeps\HeroTinker\HeroTinkerTank.blp
samurai.blp uses this path >
units\goblin\samurai.blp
samurai.blp uses this path >
units\Goblin\Samurai.blp
Remember to re-open your map, saving it.
If you still have trouble, contact the author.