Run the following command using the command line:
patch -cl -d [PHPBB DIRECTORY] -p1 < [PATCH NAME]
where PHPBB DIRECTORY is the directory name your phpBB board resides in and where PATCH NAME is the filename of the patch file which you would like to execute.
This should complete quickly, hopefully without any HUNK FAILED comments.
Where do I run this command and how? Obviously, I am not a programmer so your help is much appreciated. Thanks.