http://mponpsecu5qaqu4s7chzbldsp6hu45pwecvr72m26xbf6lo3slqo6tad.onion/docs/INSTALL.html
Place the correct patch in the parent directory containing the phpBB core files (i.e. index.php, viewforum.php, etc.). With this done you should run the following command: patch -cl -d [PHPBB DIRECTORY] -p1 < [PATCH NAME] (where PHPBB DIRECTORY is the directory name your phpBB Installation resides in, for example phpBB, and where PATCH NAME is the relevant filename of the selected patch file).