• Echoing what Gail said, if you want to free up memory by changing what SQL Server uses you need to reduce max server memory until you get it to a level you're happy with.

    Before SQL Server 2012 (so this applies to your instance), the max server memory setting did not apply to all areas of SQL Server memory, so while 56 GB would be the cap for the various caches, it doesn't include things like CLR, multipage allocations, and some other pieces. You can see http://blogs.msdn.com/b/sqlosteam/archive/2012/07/12/memory-manager-configuration-changes-in-sql-server-2012.aspx for a quick explanation.

    That's why you'll see SQL Server using more than 56 GB if you query, say, sys.dm_os_process_memory on your instance.

    Cheers!