TL;DR:
OJS 2.4.8-5 > OJS 3.2.1-4 > OJS 3.3.0-14
You have a detailed explanation in the “How to upgrade” documentation:
https://docs.pkp.sfu.ca/dev/upgrade-guide/en/#upgrading-from-2x
If you want to make visible the suplementary files, you will probably add an extra pit-stop in last OJS 3.1 (check this post).
Cheers,
m.