To remove the coupling we will need a thin 7mm spanner. We have already removed the glass jar.
We start by sliding the spanner underneath the coupler.
We then rotate the coupler whilst gently pressing the spanner against the shaft until we feel it lock onto the shaft.
At this point the spanner is holding the spindle under the coupler still.
Whilst holding the spanner tightly we turn the coupler clockwise. This is the opposite way to which you would normally turn a screw to undo it.
The Coupler could now easily unscrew and can be removed from the spindle.
To fit a new coupler simply screw the new one into position by turning it anti-clockwise. You do not need to tighten the coupler as it will tighten during use.
If the coupler is too tight to remove by hand you may need to use a pair of pliers, mole grips or a pipe wrench.
If the coupler is on too tight or you cannot easily unscrew it then the alternative way is to use a large screwdriver as shown in this video: