There are lots of ideas on Pinterest if you want to completely replace it although the picture you have posted is perhaps what you want to go for eventually. I would first try painting it all, you can get tile paint which may cover the onyx look insert. There is a product called ESP which if you apply it before paint it will let you paint anything, including plastic. We painted the mahogany fire surround we inherited with this house, we cleaned it with sugar soap and made a key for the paint with wire wool, then we applied a coat of white emulsion followed by white paint (not gloss). When we recently redecorated it we took it all out, had the gas point disconnected, DH filled in all the holes the fireplace left, replaced the skirting board and now have a wall mounted electric fire with a nice flame effect.