Going from 8.2 to 8.3 was a BIG change. Going from 8.4 to 9.x is not so big a change. Certainly some things will change and some things will be added in the new version. So you need to check the documentation and especially the release notes. If you have opportunity to test the upgrade with a machine that is not in production that would be very good. But overall I do not remember any big changes that would impact your upgrade.