Open …\Steam\steamapps\common\SpeedRunners\Content\ (Steam: right-click the game › Manage › Browse local files)
Back up Characters\Burger\animation_variant00.xnb, animation_atlas_variant00.xnb, heads.xnb, win_variant00.xnb, win_atlas_variant00.xnb and UI\MultiplayerMenu\Lobby\characterPortraits${sheetN}.xnb
Copy the zip's folders into Content\, replacing the originals (the zip keeps the game's folder layout)
Start SpeedRunners, pick Burger and skin variant 00. Verify integrity of game files in Steam puts the originals back any time.