Some time ago, te phpBB Team sent the instructions below to do a new fresh board with my existant database (posts, user, etc).
Its valid to do the same for a migration of 3.1.10 to 3.2 phpBB board?
I want to remove all mods, and reinstall from zero...
Backup all board files and the database.
Download the full package.
Unzip to your desktop and open the phpBB3 directory.
Remove (delete) the config.php file, and the /images and /files directories from the package.
In Administration Control Panel (ACP) > GENERAL > Board Configuration > Board settings
Default language: British English
Default style: prosilver
Overide user style: Yes
If spambot countermeasures are enabled: Administration Control Panel (ACP) > GENERAL > Board Configuration > Spambot countermeasure if the installed plugin used is not GD image, GD 3D image, Simple image, Q&A, or reCaptcha, then change it to one of those.
Clean the database
Download and uncompress the Support Toolkit
Upload the stk directory from Support Toolkit package to the root of your board installation.
In your browser go to http://www.example.com/yourforum/stk, login if necessary.
Using the menus navigate to ADMIN TOOLS > Database Cleaner and run that tool.
Via FTP or SSH delete everything from your board installation on the server EXCEPT for the config.php file, and the /files, /images, and /store directories.
You can also, optionally, delete the /store/mods directory, if it exists (it contains the MOD packages installed using AutoMOD).
Via FTP or SSH upload the remaining files and directories (from step iii above) to the root of your board installation on the server overwriting the existing files.
In your browser go to http://www.example.com/yourforum/instal ... update.php
Let that run to completion, it may need to be continued several times.
Via FTP or SSH delete the /install/ directory from the root of your board installation.
If you use languages other than the standard British English you will need to find new language packs, upload those to the board, and install those languages again: ACP > CUSTOMISE > Language Management > Language packs.
Only use a good FTP or SSH client, such as FileZilla, to transfer the files. (File transfer utilities provided in host control panels can cause problems.)
You now have an up to date board containing all your users and posts.