This plugin will help you convert your forum posts, threads, categories, users and tags from the vBulletin forum to bbPress plugin literally in minutes. https://wordpress.org/plugins/cms2cms-automated-vbulletin-to-bbpress-migrator/

1. CMS2CMS:
Automated
vBulletin to
bbPress Migrator

3.
vBulletin to bbPress. With No
Errors and Gaps

4. Having an active forum has become the top priority for many
website owners targeted at retaining their loyal readers and
attracting potential ones. vBulletin and bbPress are popular forum
boards that allow webmasters to stay in touch and hold a solid
interaction with their readers.
vBulletin is an efficient and robust forum package that is used all
over the globe by fairly big companies. It is packed with a huge
number of options to make your forum meet your specific needs.
However, all the bells and whistles of the platform have their price.
Being a commercial software – vBulletin is becoming less popular
and many users are leaving it in favor of free, but powerful
bbPress. bbPress, alternatively, is both invaluable and priceless,
providing great possibilities for online interaction at no price at all.
Usually users find a lot to like with the platform – however, it keeps
focused on the ease of use, ease of integration and fast speed.
Millions of people worldwide gravitate towards the platform due to
its flexibility and strong security features.
Ready to migrate to bbPress? Then look no further than CMS2CMS
automated migration service that will transfer all your vBulletin data
to bbPress swiftly, accurately and with your minimal involvement.
Get know all the tips and tricks of successful switching across
above­mentioned forum boards from the migration guideline
provided below:

5. 1. Download the Plugin.
Initially, download “CMS2CMS: Automated vBulletin to bbPress”
Plugin on the official WordPress plugin repository and save it on
your PC. Then:
● Go to your new WordPress website admin panel
● Right within dashboard find “Plugins” ­> “Add New” and
upload the file.
● As soon as the file is installed, click “Activate” button.

6. 2. Create an Account.
Register your CMS2CMS account. You just have to provide your
username and password.

7. 3. Establish your Source and Target Sites.
Select your current and new types of platforms (vBulletin and
bbPress correspondingly). When finished, type in the URL
addresses of both your forum softwares.

8. 4. Select Migration Preferences.
Specify from the list of options those you’d like to be performed
during the migration process. Remember that you can convert not
only users and categories, but also threads, polls and replies.

10. 5. Run Demo Migration.
To proceed with the further steps – try free Demo Migration to see
the service in progress.

11. 6. Initiate Full Migration.
In case you are totally satisfied with Demo – perform Full Migration.
After the final click, your vBulletin website content will be converted
to bbPress.
That’s it! Congratulations! Now you may check the results of the
conversion (that will certainly outperform even the most creative
and forward­thinking expectations) and start using all new
opportunities that bbPress has to offer.