One of the method is by performing a query on the server using below T-SQL query;
select @@version
There will be full versioning details of the SQL server like below;
Microsoft SQL Server 2005 - 9.00.3073.00 (Intel X86) Aug 5 2008 12:31:12 Copyright (c) 1988-2005 Microsoft Corporation Enterprise Evaluation Edition on Windows NT 5.1 (Build 2600: Service Pack 3)