Deactivate Orgs You Don’t Use

When an org has outlived its usefulness and it’s time to move on, you can deactivate it. When you deactivate an org, you have 30 days to change your mind and reactivate it. After 30 days, the org is locked, and you must contact Salesforce Customer Support to reactivate it. After 60 days, the org is permanently deleted from Salesforce servers.
Available in: Developer and Database.com Editions

User Permissions Needed
To view company information View Setup and Configuration
To deactivate an org Modify All Data

From Setup, you can deactivate an org from the Company Information page.

If the org has released a managed package, you can’t deactivate it. Contact Salesforce Customer Support for assistance.