I need advice on my options for upgrading my drill press

[th62]

Arbors are Morse Tapers, MT2, MT3, MT4 and so on, but why do you want to upgrade it? The other end of the arbor that fits in the drill chuck is usually Jacobs Taper, JT6, JT3, etc, or B10, B16, etc. MTs are sized to suit the spindle and spindles are sized to suit the drill press body.
You can't 'upgrade' them, assuming you want a bigger diameter spindle, or longer stroke, the only way you can upsize that is to buy a bigger drill press, same for an MT. If the column is too short, you can extend the column, that's an easy job, but realistically you'd be better off upgrading to a pedestal drill.