I agree fullheartedly with what most people on here said, do not alter this ring, especially if this is an antique the value comes in part from the entire piece and resetting it would take away the integrity and some of the value not to mention the sentimental value. Also, it is very important to have this piece checked by a professional and verify the authenticity of the stone especially as this would be a very valuable jewel but it is crucial to have it verified that it indeed is a diamond. I would also resize it if you must, keep it and wear it for occassions if you find it too large. I think it looks great on you, not too big but of course you may feel it is too big if you are not used to wearing such a large stone. I too would wear it for occasions. Beautiful piece and fits your beautiful hand so well! Please keep us posted about it, what you find out and whether you have anything done to it.