To make the original pickups better, you need to rewind them and probably replace the magnets too. And that might not do much. I'd just replace them unless you feel like experimenting.
I had an Epiphone Sheraton II come to me with similar complaints. I replaced the pickups, and also the bridge, tailpiece, and tuners. I wasn't making pickups at the time so we used Duncan Alnico IIs. That guitar sounded 100 times better. The wood working is not bad, but the parts suck.