I had one similar to that for a while. They're OK bikes, a bit heavy and not the best ride, but serviceable. I converted mine to a 1x5 townie setup before I sold it. If it still has the original disc brake in the rear, the first thing I would do is remove it - they are pretty useless and quite heavy. Get a set of modern dual-pivots and start from there; at least you'll be able to stop. Single-speed is not a bad idea either.