For Showtime, the process is a bit different because the current plan needs to be canceled and then reactivated. Additionally, existing Hulu users will need to be on the ad-supported plan ($6.99 per month), not have any add-ons like Showtime or HBO, and be paying for Hulu directly and not via a third-party platform like Roku or Amazon to switch their billing to Spotify. Existing Hulu users need to agree to switch their billing over to Spotify while signing up for a Student plan. Spotify notes that users can activate these free subscriptions on existing Hulu/Showtime accounts or create new ones.
Once a Spotify Premium Student subscription has been purchased, users can immediately activate the free Hulu or Showtime plans to start streaming their favorite shows. Related: Favorite Music Guru For Spotify: How To Find Your Top Artists & Tracks