SQL Server database won't shrink

I have a 31 GB database I got from a customer for a project. I'm coding and keeping the database in a 80GB Win7 VM. I got the db file and imported the database from that, and found that the space was being eaten up mostly by one table, with 240,000 images. I dropped most of those rows and now have 29,000MB available. I can't perform lots of functions because the drive is down to it's last few GB, and there are still a lot of records to modify (I'm changing a data type in several tables, but keep getting a active_transaction error). It's not shrinking via DBCC_SHRINKDATABASE(0) or Tasks > Shrink > Database or Files. It only shrinks to the size of the database when I first got it, it seems. How do I get it to release that space? If I can', can I export what data is still there to a smaller database, and then restore from that?

Running SQL Server 2012 and Management Studio.

Thanks,

Tony