PHPBB is the world's #1 free community (forum) building Open Source Web software licenced under GPL. PHPBB is the first choice of web developer who want to deliver a easy to use , secure forum which offers cutomization like changing theme, creating custom login and registration pages and if you have guts then you can change it your ways.
click on language entries
click on british language / or your default language
and if want TERMS_OF_USE_CONTENT
Now you can save it but when saving it ask submit and download the file or you can update file using FTP details when select submit only, if you have FTP details then you can easily change it but if you running it on your localhost then download the ucp.php file and overwrite ucp.php file in phpbb folder under language->en->ucp.php