To Download SQL Server 2012 Express:

Please refer Link:

https://www.microsoft.com/en-my/download/details.aspx?id=29062


Click Download.


Choose x64 if your Server PC is 64bit or choose x86 if your Server PC is 32bit > Click Next.


To Upgrade from existing SQL Server 2008 R2 Express to SQL SERVER 2012 Express

Step 1 - Click 'Upgrade from SQL Server 2005, SQL Server 2008 or SQL Server 2008 R2'


Step 2 - Click Next.


Step 3 - Tick Both Option >  Click Next.


Step 4 - Select Instance > Click Next


Step 5 - Click Next.


Step 6 - Upgrade Start


Thanks,


To know How to Install SQL Server 2012 express.