You cannot change the pages associated with BuddyPress in Add New or Edit Post/Page panel – page template. You would have to change the HTML markup of the specific component’s template file. What theme are you using?
I’m using Navi by NewWPThemes.
Did you install BP Template Pack plugin which is required to make your theme compatible with BuddyPress? Then did you go through Appearance > BP Compatibility process? In Step 3 of the process, that’s where you can change HTML structure of the BP template files transferred to your WP theme in server to be full width or any other layout configuration.
I was had same problem with Heresteve2, I solved this like @mercime
Sorry for posting this somewhat randomly but I cannot for the life of me find the ‘create new topic’ button for this forum – I need to report the fact that the pagination on the buddypress.org website is broken – can’t get past page 1! Thanks for showing where to look anyone!