Well, here is how it goes then.

Make all the lod models. Then select all of them(the order is important here), and go to EDIT->LEVEL of DETAILS->GROUP.

Then open up Outliner, and you should have a new group there. By default it has name LodGroup.

Now you can animate THIS lod group, set the distance fom where difrent lod levels appears. To do that, select this LOD group, and in channelbox, there you have option called 'Treshold[number]'. The number represents the LOD level. Now you can set here distance. AND that's pretty much it. Just don't forget to select the lodGroup, not the model itself when animating.