I have a dyson dc 05 and a wire has come

In the centre of each wheel there is a different colour plug. This must be removed before the wheel can be pulled off. I used a small screwdriver to prise it out. You will probably damage the plug in removing it but they are easily available online as a replacement. You will then see two screws holding the case together. You need to undo both sides plus the screw on the top.
(If you think you may have a loose connection, then it could be the motor brushes have worn out and need replacing)