To edit or delete existing content, log in and then bring up the page you wish to edit. Look on the page for an "edit" tab. Depending on your user permissions, you might see this on all pages or only on certain ones.

Clicking the edit tab will bring up a page with a form for changing the page. Here you can change the text and settings. Once you have the text and settings in a suitable form, click on the "Submit" button on the bottom of the form.

If you wish to delete the page (and you have appropriate permissions), click on the "delete" button near the bottom of the form. You'll get a second chance to confirm that you wish to delete the page, or to change your mind!