You can edit or delete a note that you posted on your own profile. You can't edit notes other people leave on your profile, but you can delete them. To edit or delete a note, click your name/picture in the orange bar at the top of any page, go to My Profile and click Notes. Find the note you want to make changes to and click the pencil icon to edit it or the trash icon to delete it.
Once you submit a note on someone else's profile, you cannot go back and edit or delete it. You can contact that person and ask them to delete it, but they can't edit it.