To reglaze tiles, take off old caulking using a silicone digester, etch porcelain tiles with acid paste, and apply degreaser onto the tiles. Prime the surface using an epoxy primer. Choose the resin you want to use for the tiles, apply it, and let it dry completely. Coat the tiles with polyurethane.
Home improvement stores usually have silicone digesters for caulking removal. Make sure to follow the manufacturer's directions carefully. The caulking has to be gone completely before you can continue to the next step. Always use gloves to protect your skin when working with acid paste, as it can harm you if it gets on the skin. Be careful not to get the paste on other areas of the bathroom, as it can damage other surfaces.
Make sure to apply the degreaser compound to all the areas you are going to reglaze, and allow it to dry completely before proceeding. When choosing an epoxy primer, pay attention to its application guidelines, as some of them are sprayed onto the surface, and some of them users need to apply using a roller or a brush. Again, make sure to apply it to the entire area. Resin comes in two types, one that takes one day to cure and another that takes three days; the second kind is better. Polyurethane makes the tile surface shinier.