The clamps are glued on. If you redrill the hole you see slightly larger you can tap the clamp off with a rubber mallet because you're breaking the glue seal IF you're very lucky. Otherwise you will have to cut the clamp off and fit a new one.
When you fit a new clamp, don't go mad with the glue because then you'll be able to remove it easier when it's worn. OR you could modify the Ionics ergolite clamps with parts of Tuckers pennel clamps so they lasts a lot longer.