A 48t chainring is almost exactly an inch larger in diameter than a 42t chainring. Measure 1/2" back along the chainstay from the inside of the 42t chainring. That is where the 48t ring will sit. Depending on your chainline now, the new ring might move in or out, so you may want to measure your chainline as well.

You can quite likely fix what you have quite easily and inexpensively. You'll know for sure once you get it disassembled, and bottom brackets aren't rocket science. Assuming you had a decent chainline beforehand, I would work with what you have rather than getting into the hassle (and cost) of getting everything lined up with new parts.