In all honesty the quickest way is to just slice and reposition in paint. I'm sure there are converters out there but by the time you've downloaded it you'd be done. Just cut 256px wide bits off the tilesets and paste them end to end. An easy way to do THAT is to draw the tiles in the map editor as if you were mapping, leaving a white border, then print screening. That makes it very easy to rearrange tiles too as you're already in a tile mapper.
Characters are tougher but there are converters out there for that.