It's a comon problem, and a piece of cake.
That ring with all the numbers on threads on like a filter. To remove it you can often just use a eraser, or a bathroom plug to grip it, and unthread it.
I wouldn't recomend it, but I had a miserable one, on a lens given to me, so I notched it with a dremal, then used a screwdriver to remove it (that one was a real bugger of a lens)
once removed you'll see either 3 or 6 screws. Only 3 of them hold the ring on, and you'll see that they're loose.
just tighten them back up, and put the numbered ring back on. Your done