SQL Server Databsae from SINGLE USER mode to MULTI USER

SQL Server 2012  Right Click on  DB > Properties > Options > [Scroll down] State > RestrictAccess > select Multi_user and click OK.

SQL Server 2008 R2 and earlier

Script to change the database from single user to multi user

--Script
use master

GO

-- Find the active sessions and kill it

select DB.name, DB.dbid, spid, login_time, nt_domain, nt_username, loginame 

from sysprocesses Process

inner join sysdatabases DB

on Process.dbid = DB.dbid

where DB.name = 'Databsae Name'

GO

kill spid

--Execute the below stored procedure to change to multiuser

exec sp_dboption 'Database Name', 'single user', 'FALSE'