I think that there are two screws located on the back two sides of the upper roller brush cover that need to be removed. The front of the same part is held together by a latch. The way to separate the top from the bottom is to lift the top cover up from the back where the screws were and lift it up and forward and keep rotating it until it comes free in the front. The height adjustment knob should just fall out at that poiint. Hope this helps.
www.bobsroswellvacuum.com, September 2008