Adjusting height on old dining room table

Hey guys, I'm a total novice here hoping someone can give me some advice.

Wife just bought an old antique dining room table, but we've realized it's probably about an inch too low for our current chairs. So we bought some castors to install on the legs to raise it slightly. Only problem is we didn't check the bottom first and have now discovered these circle metal raiser-thingys (yes, I'm a novice) already installed on the bottom. THey seem very firmly attached....we can't tell whether they're screwed in or glued.

So not sure what to do.....try and find a way to remove the metal raiser....or jsut shave off an inch or two and reinstall some sort of wood extension to the bottom, or??? See attached pic.

I really just want to get rid of the thing at this point, but my wife loves it...