With the dial facing you, push the toaster base up and away until the base is just over the lip of the shell. This will disconnect the browning dial from the rest of the toaster.

When reassembling the toaster, make sure that the back of the dial lines up with the slot, both in position and orientation (the dial and slot are not perfect circles - they have a notch).

The only object holding the shell onto the toaster now is the grey part of the lever.