Angle Grinder.

Seriously ...

Remove rear bumper for easier access to the two bolts that mount top of
towing plate to chassis rail / crossmember, then two bolts on each
chassis rail that hold the two 'arms' of the tow bar.  It's highly
recommended to replace these bolts and nuts and in my case the easiest
way to remove them was with an Angle Grinder.  ;)

Re-fitting is a reversal of the procedure ... ;)  Though, in my case, I
found it wasier to fit the plate loosely first, then the arms and
tighten bolts up when all is straight.

Not that mine ever stays straight for long ... I've bent yet another
[1] bloody towbar arm.  I think I'll have to make some heavy duty
things up or get a Southdown tank guard so I can remove the towing
bracket altogether ... ;)

[1] Third one in six years or so.