I had a prefacelift X5 before and it had the round ring and all you do is feel your way around the ring and it will have notches on it and all you do is pull REALLY HARD. I had to really struggle with mine but it will come off. Now I have a facelift X5 just like yours, it has a rectangle ring but I have yet to try but i'm sure it is the same way.

Just pull hard on the ring on the notches using your fingers and BE PATIENT

thats exactly what i would recommend and do