Hmmm...you have your work and research cut out for you. I would begin by completely removing everything from the tank and rinsing it out. That goes for all filters etc. Get all equipment ready to go. Next, decide what type of SW tank you want...FO, (not recommeded), FOWLR (good choice) or reef (my personal fav). Next, research things like filtration, lighting, fish, etc. depending on what you want. It is pretty much starting from square one. Look into the fishless cycle method for getting your tank up and running.