You can edit and delete annotations you have created by tapping on an annotation to select it. When you do, you will see a popup dialogue box that will allow you to edit the style of the annotation or delete it. It will also show you the name of the annotation author and if there are any comments attached to the annotation.
From this view you may choose to delete the annotation or edit it. Different tools have different attributes that can be edited. Refer to individual tools for those editable attributes.