As the Account Owner, you can edit stages by navigating to the Admin > Stages screen.

On this screen you can rename and reorder stages.  You can also add new stages or delete stages you no longer need. 

To rename a stage, click the edit icon next to a stage, to delete a stage click the delete icon:

If you want to reorder the stages, drag a stage using the grip icon to the left of the stage and drop it somewhere else in the list:

NOTE: The "Lead", "Closed" and "Trash" stages are used by the system, and cannot be renamed or deleted.