SQL Server upgrade single instance I have a server that is running SQL Server 2005 Express.

It currently has 2 instances of SQL Server running.


Instance 1 runs some old legacy software that is not supported by me.
Instance 2 runs my software. 


Is it possible to upgrade instance 2 to SQL Server 2008 R2 Express independently of instance 1, i.e. keeping instance 1 on 2005 while instance 2 is upgraded?
Absolutely, when you run setup for SQL Server 2008 Express choose the instance you want to upgrade. By doing so you only upgrade that instance to SQL Server 2008 R2. Other instances will stay on 2005 however any client tools like Management Studio Express will be upgraded to 2008 R2.