Upgrading is not a problem.
Keep in mind that your version is perl based.
Where the newest version is php scripts and require a mysql database.
Keeping the posts is not a issue.
If you can verify your license with ubb then all you will need is member access for upgrades for 59 dollars.
What I am not sure of is you may need to upgrade twice.
Once for ubb classic 6.2.1 to ubb classic 6.7.3
Then upgrade to ubbthreads 7.5.6.
both versions are in the member area for download.
Last edited by Ruben; 06/30/2011 1:00 PM. Reason: typo error
