How do I Change SQL Database from Single_User to Multi_User Mode

How do I Change SQL Database from Single_User to Multi_User Mode:
Sometimes, we have the need to set the database in Single User Mode to do some upgrades or blocking all the access to the Database.

Set the Database to Single User Mode :

ALTER DATABASE [DBNAME]
SET SINGLE_USER
WITH ROLLBACK IMMEDIATE

When you to set it back to MULTI_USER , you get the following error.

ALTER DATABASE [DBNAME]
SET MULTI_USER
WITH ROLLBACK IMMEDIATE

Msg 5064, Level 16, State 1, Line 1
Changes to the state or options of database ‘[DBNAME]’ cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.

Because the database is in Single User mode and available one connection is already taken.
One Option is to find out which process is using that one connection and you take over that connection.

Get the Process : (SPID)

use master
GO

select
d.name,
d.dbid,
spid,
login_time,
nt_domain,
nt_username,
loginame
from sysprocesses p
inner join sysdatabases d
on p.dbid = d.dbid
where d.name = '[DBNAME]'

-- Kill the SPID you get from Above Query
KILL [SPID]

-- Then you execute the statement to set it to MULTI_USER.

ALTER DATABASE [DBNAME]
SET MULTI_USER
WITH ROLLBACK IMMEDIATE