Important, make sure you run update_to_latest.php after every upgrade, and check your forums functionality after each upgade.
NOTE: the update_to_XXX.php
files were numbered up to and including 2.0.11, after that (going from 2.0.11 to 2.0.12 and up) the name of the file was changed to update_to_latest.php
(depending on the update you are doing) can be found in the install folder inside each update. Load the install folder to your forum root.
Using your browser, go to:
if you are updating anything below version 2.0.11).
Once this is done, delete the install folder.
It would be smart to back everything up after each update so that if you screw it up, you can go back to the last working version and try the upgrade again.
You can find all versions of the phpBB files (1.0.0 to 2.0.19) at:
LINK>> Source Forge <<LINK