You can edit, copy or delete sessions when in edit view - ie Program Builder.
Click on delete to simply delete the session.
NB - you cannot delete a session with abstracts attached to it (ie - in the Submissions field below).
Clicking on copy
will copy over all the session details, which you can edit to create a new session. This can save time when there are multiple similar sessions.
Make sure you click save to retain the new session.
Clicking on edit
will display the session in edit mode. Make your changes and click save.
See also Creating a session.