I'm studying  Admin Trail - Migrating to Lightning Experience modules. I use a developer Org, to practice and to do challenges. 
But I don't see how enbaling Lighting Experience. In this module https://developer.salesforce.com/trailhead/lex_admin_migration/lex_migration_introduction/lex_migration_introduction_administration, it's indicated that : "To enable Lightning Experience, go to the Lightning Setup page, which is accessible in Setup by clicking Lightning Experience" but i can't find the Lightning Setup page.
Is Ligntning Experience included in Developer Edition? if Yes, How can i enable it? if No, When it will be included in Developer edition and how can i get it?
Thank your for your help.