I remove rings like that all the time at work (I repair air, hydraulic, and electric power tools).
Get a cheap set of O-ring picks from the local Harbor Freight or auto parts store -- shouldn't cost more than five bucks. CAREFULLY work the point of the 45 degree pick under one end of that ring, and pry it UP. Once it's up a bit, the whole ring should start moving and you'll be able to work it out of the mount. Do, please, keep track of which side of the lens element is forward...
Edit: the post above come up while I was typing. From the photos, it doesn't appear this ring has a groove, so you don't need to worry about getting it out of the groove. It appears Zeiss went full penny-pincher on this one, and figured the ring would have enough friction with the barrel to keep the lens element in place.