In Safari:
Click on the Bookmarks icon.
Select the "Bookmarks Bar" folder.
You'll see all the bookmarks that are displayed in the bar under the url address space.
Click the "Edit" button.
Select the entry you want to edit by pressing near the ">" symbol on the entry line.
You'll then be able to edit the bookmark's title and url and event its location if you want.
When finished, click on the "Bookmarks Bar" button to get back to the previous section.
Click on the blue "Done" button to save your changes and then exit from the bookmarks menu.
You're done!