Upgrade path from 5.9.1 to 6.6?

Needing to upgrade from Defender version 5.9.1 to version 6.x. would I need to step the upgrade(5.9.1 > 6.0 > 6.6) or will I be able to directly upgrade to 6.6?

looking for suggestions on the safest path to upgrade and any known gotchas? thanks!