It's a job you can hire out too, it's completely possible to completely nerf your install with a bad upgrade.
But as Ruben pointed out it's a long trek from where you are; the importers where designed to run on the latest builds of the "old" software, so you have to be semi current there, so you'll end up having to do (or have done):
1. Upgrade to the latest UBB.Classic.
2. Install and Import to UBB.Threads 7.2 (otherwise all of your members will be moderators; the group permission system was updated in 7.3 to add Global Moderators and the importers where never updated accordingly)
3. Upgrade to the latest UBB.Threads release.
4. Install the "Redirect" scripts for UBB.Classic (they're in the file with the importer data) so that bookmarked locations and search engines can still locate old posts on your new forum.
