How can I use different .NET Framework version?

How can I use different .NET Framework version?

Hi.
VSTA>
i want use open xml sdk2.5 .
This version will only work with .NT Framework4.0.
but VSTA .NET version 3.5.(It supports to version 2.0.)
How can I use it?

This is a migrated post! Originally posted on 04.05.2016 by user backjahyun. Please be aware that information can be outdated.