If it's a bridge pin, it can definitely be pushed up through from the inside by putting your hand in there, finding the end of the pin, and pushing up. If it hurts your finger, put a piece of leather or something between the end of your finger and the pin as you push on it. It will be easier to remove if the string is not pulled all the way up...that is, if the "barrel" end of the string is not snugged up against the hole on the underside. A loosened-off string can usually be pushed down farther into the hole to achieve that.

polly - It will not be too easy to locate a new top for an old Ovation, and it will be expensive. A luthier can make a new top for it, but that will be expensive too. I'd just get another guitar if I were you.