BuddyPress.org

Hi, the first few weeks I used only wordpress but now I want to build a community hence I’ve installed BuddyPress.
Following problem appeared:
When clicking e.g. the ”activity” button, the browser says ”Objekt nicht gefunden” / ”Object not found”. I’ve already found out that there might be a problem with the ”site_url”. Named is set to the URL ”www.biggaa.de/wordpress”; the right URL is ”www.biggaa.de”.
So how can i change the ”site_url”?
Thank you in advance and greets from Germany!