Starting from SQL Server 2008, you can use the following SQL query to get the version information of your SQL server.
SELECT @@VERSION
Execute the command in SSMS and it will show output like this
Microsoft SQL Server 2014 - 12.0.2000.8 (X64)
Feb 20 2014 20:04:26
Copyright (c) Microsoft Corporation
Express Edition (64-bit) on Windows NT 6.3 <X64> (Build 17134: )
This means I am now using SQL Server version 2014 X64 bit and other information.