I have a client that has a recently expired SQL Server 2008r2 Enterprise Evaluation edition. I've been tasked to get it licensed and running SQL Server 2008 r2 Standard. How can I achieve this?
You have to install SQL Server 2008 r2 Standard edition side by side (if you want to do it on the same server) and then move the database using backup/restore method.
Below is an outline of what needs to be done (if you want to do it on the same server without installing a side by side SQL 2008R2 instance).
Also, Unless you're using Enterprise-only features, you should be able to use detach and attach method from Enterprise to Standard.
Refer to answer by Jonathan here.
Also, refer to this approach with scripts... BUT WITH EXTREME CAUTION !! ... it uses detach/attach method and if you are using any enterprise features (which wont work in Standard edition) then the attach wont work.
Also, refer to Version and Edition Upgrades Matrix.