To Download SQL Server 2012 Express:
Please refer Link:
http://www.microsoft.com/en-my/download/details.aspx?id=43351
Click Download.
Choose x64 if your Server PC is 64bit or choose x86 if your Server PC is 32bit > Click Next.
To Install SQL Server 2012 Express.
Step 1 - Click 'NEW SQL Server Stand-alone installation or add features to an existing installation'
Step 2 - Click Next.
Step 3 - Tick 'Perform a new Installation of SQL Server 2012' > Click Next.
Step 4 - Tick both option > Click Next
Step 5 - Click Next
Step 6 - Change Named Instance to QNEBSS > Click Next
Step 7 - Click Browse
Step 8 - Insert 'system' > Click OK.
Step 9 - Click Mixed Mode > Insert Password 'QnE123!@#'
Step 10 - Click Next
Step 11 - Start Installation
Thanks.
To know How to upgrade existing SQL Server 2008 R2 express to SQL Server 2012 Express