If you'd like to make a change to something you've posted, visit the page where you posted the memory. Scroll to the memory that you'd like to edit or delete and once there, you should see options to 'Edit' or 'Delete' the memory. (If you don't see those options, remember to check that you're logged-in!).
Once you click 'Edit', you'll be able to update any part of the memory that you shared.