Originally Posted by IthaDan

If youre clamping the wheel near the front pf the dropout, you'll probably need a link or a half link to go from 16t to 19t. If you're clamping near the end (away from the crankset) you should be fine.

As far an changing chain rings, look into new cranks, finding a chainring for those cranks (if you can even change the chainrings) will be a long search and most likely expensive. You have a bog standard square taper bottom bracket, go nuts.