It hasn't gone well, I thought I had been so careful, but I forgot to add the contrib file. I ran the update_to_latest and it said all was fine, but will not show the Admin panel, just keeps saying "ensure the install and contrib folders are deleted". I replaced the install directory, added contrib and ran updated to latest again, and the same result: a page showing no errors, 2.0.19, but will not move past the "ensure..." page (a phpBB page with the forum logo).
I deleted the install and contrib files and it said I had to login again, now it says:
Fatal error: Call to undefined function: phpbb_clean_username() in /home/.badlands/laingsoc/laingsociety.org/giardino/login.php on line 57
I posted this on the phpBB forum but no one has replied, if anyone who's sharp with phpBB happens to read this, I would be really grateful for any suggestions.