How to remove cistern lid with dual flush toilet

I'm having trouble with my toilet, its flushing my itself and when I do flush it, it keeps flushing for ages until it eventually stops.

In order to fix the above, I need to get the lid off the cistern. But I've got a dual flush toilet so can't just remove it. I've had a look on youtube, but all the dual flush mechanisms are different to mine. On mine there's a chrome ring with the push button releases attached to some plastic bits underneath it.

I've tried to unscrew it but it doesn't budge enough to be unscrewed.

Can I just remove the chrome ring? I've tried but its fairly tight to get off. I don't want to use force and break something, adding to my problem!

Any help would be much appreciated, I have some pictures attached.