We are looking here to access the area near the gimbal lock arm spring on the Dyson DC40, DC41, DC42 and DC43.
To do this involves getting to the wheel/ball mechanism on the machine.
In order to access this, you use a pair of long nose pliers to remove the glamour cap in the wheel, you insert the long nose plyers into the holes in the glamour cap and turn it anti clockwise.
Having done that, you expose the mechanism below that looks like this:
Then you need to insert the pliers into the holes on either side of the plastic cap underneath and unscrew the wheel using the pliers.
Notes: The DC40 and the DC41 are the model designations for the new generation (2012) of Dyson Ball. You can read about the differences between the two machines here: What is the difference between the Dyson DC40 and the Dyson DC41?
The DC42 and DC43 are non UK variants of the same models.
So essentially, the DC40, DC41, DC42 and the DC43 are the same machine which comes in two different sizes.