software upgrades

Hello can you please help I'm having trouble upgrading the software from the latest download on the ajax site according to the instructions when you go into upgrades it should recognise that you have the file on the A: drive and should load automaticlly it dosent happen on mine can anyone give me any ideas also is there much differance in the latest version 8.23 to 8.21 also I have a colluege who has bought a machine with a Centroid control running version 4 he would like to know does the ajax software upgrade onto the Centroid control, hope I can get some answers Cheers Colin