How to use AssetBundle on Android for external download

Hi. How can i use asset bundle to download filest textures and prefabs and put in assets folder. For an example lets say i have a project with a prefab and a texture. The prebab have 70 mb and the texture have 2 mb, and i make a scene when i use that prefab and that texture. When i bulid the final apk it will have 70 mb. To make it small i need to load that prefab and that texture with assetbundle, and that's my question: How to do that. Because if i use a code like this:

function Start(){ var download:WWW=WWW.LoadFromCacheOrDownload("my link", my version); yield download; Instantiate(download.assetBundle.mainAsset); }

and i make a unity 3d file with the prefab an the texture this code will instantiate in the scene view the prefab and texture not in the project view to use them in more scenes. Please HELP me. Thanks.