Transact-SQL:
To remove a SQL Server database mirroring session using T-SQL, run this code from either database mirroring partner:
ALTER DATABASE [Database_Name] SET PARTNER OFF
SQL Server Management Studio:
To remove a SQL Server database mirroring session from SQL Server Management Studio:
Connect to the principal server instance -> Right-click the database -> select Tasks -> click Mirror:
Click Remove Mirroring:
Click 'Yes' to confirm: