Any existing bookmark can be edited by choosing the bookmark in section 2 of the add bookmark form. You can edit any of the information and it will be updated when the add button is pressed. You may also edit the folder keywords, which will change the name of the folder.
If you prefer, you may edit the bookmarks in the tracker by pressing the "show in tracker" button, but remember the naming syntax, so they will show up. There is a limit of 10 (0-9) bookmarks per folder.