Yes, you can delete a plan.
Keep in mind that the benefits of that plan will continue for any subscribers until the month they paid for expires. This will likely not be at the end of the calendar month. While Makers (you) receive subscription payouts at the start of each month, guests are always charged on the date at which they first subscribed.
So if you delete a plan on October 20th but the guest’s plan renewal date was the 18th, that guest’s benefits will extend through November 18th.