How do I get to the beater bar of my 'Kenmore Progressive' Vacuum open to change the belt?

Help! I cant get the casing open to get to the beater bar of my cannster to change the belt. It is model 116 52612201. The casing says 'Kenmore Whisper Belt'. I removed the screws and tried to pop the sides but it wont come apart. How do I open the darn thing?How do I get to the beater bar of my 'Kenmore Progressive' Vacuum open to change the belt?:)