Transitions are available from the transition list that appears when targeting a link, or in the gesture panels for linked layers in the inspector. There is also a transition manager available from Edit > Transition Manager.

The transition manager provides an overview of all the transitions in your document and allows you to edit their names and delete them.

In the standard transition list, you can rename a transition by double clicking it, delete a transition by selecting it and pressing delete and duplicate a transition by right clicking it and choosing "Duplicate".