Knowledgebase
How to change or remove the site description and name in phpBB3
You can change or remove the site description and name that appear in the upper left corner of the frontend of your phpBB3 site from the administration panel.
After you log in to the admin panel, click on the Board settings link on the left side of the General tab page. On the Board settings page change the text in the fields for Site name and Site description to whatever you wish. Then click on the Submit button to save the changes. Refresh the frontend of your site to see the result.
You can also check out the tutorial on changing or removing the phpBB3 site description and name.