Special Note: The importers to the new product (UBB.Threads7) requires that you run the latest build of your originating product (in this case, UBB.Classic 6.7.x).

The Import
The proper upgrade route is as follows:
1. Download UBB.threads 7.x (full install file) AND the UBB.Classic 6.7.x importer and extract them to your hard disk.
2. Install UBB.threads 7.x in a NEW directory (UBB.Threads7 is a completely different product than UBB.Classic 6.7, thus, it is not a simple "update new files and run through the control panel" upgrade).
3. Go through the new install procedure (yourforums.tld/forums/install/install.php) until you reach the "create admin user" screen then click on the "create tables" link (do NOT click on the "create admin user" link).
4. Run the UBB.Classic 6.7 to UBB.threads 7.0 importer.
5. Import Complete.

Re-Using your old location
As UBB.Classic is a perl script, and UBB.threads is a PHP script, you cannot run UBB.threads from the CGI-bin (on most hosts anyway). You can however run it from the "Non-CGI" directory, which will be covered below.

If you want to re-use your old directory, simply delete (or rename) your old forum (Non-CGI) directory, and then rename the directory which houses UBB.threads 7.x; any updates to paths will need to be made to the config.inc.php file in the UBB.Threads7 includes directory.

Redirecting to the new software
Now, if you want to redirect all requests from the old directory, do the following:
1. Open the redirector files which came with the importer and edit the line that points to your install directory and set the url accordingly.
2. Upload the files to your OLD install directory.

It should be perfectly safe to upload these files into your UBB.Threads7 install directory (if you opted to use the old install directory in section 2) as UBB.Threads7 does not use these file names.

Conclusion
Now any requests that go to your old forum location/files should be redirected to your UBB7 install.

Links
UBBCentral Install Documentation
UBBCentral Documentation

NOTE
Please be sure to delete the install/ directory from your forum directory after your installation as you don't need other people trying to run it as a fresh install. You should do this after any fresh install or upgrade.

For reference, here is the complete Install Manual found in the Documentation section. See also any readme files included within the Threads' .zip files.

In addition, after installation, you should "delete the install/ directory from the server [or at least delete the files within it]. Leaving those files on the server could cause problems at a later time."

Added a note here as well about the install directory.

also added the links you provided

Assuming I put the new version in a different directory than the old version, can I install the new version and leave the old version up and running - take a couple of days to play with the style to try and get the look that I want - and then import the posts and members from the old version?

Yes, thats what most of us did

My old forum has remained up -- in read-only mode -- since I switched to Threads in October...

I've had the redirectors in place since private beta1 of UBB7.0; i recently just set them to a permanent redirect vs temp

The redirectors only work for classic I believe - on a couple of threads imports that I have seen they do not work

Thanks a lot guys - It sets my mind at ease

I guess I will finally make the move in the near future.