How to remove light fittings

[Escapade]

I am unable to open the cabins light fittings. (See picture)Tried to pull out unsuccesfully and i am afraid of damaging it.
Can any one help?
Many tks.
Oliver

[Yngmar]

They look like my old Hella ones. You open them by rotating the clear part past its "off" setting (counter-clockwise I believe) with some force. It will unlock and drop right out and reveal the screws that hold the metal frame.

[Escapade]

 
Thank you Yngmar.
They are Hella and your suggestion is correct.
To be precise you need to push the transparent up while rotating beyond the off point.
Now i can change the bulbs...