Where can I shrink database directly from Central admin (SharePoint2010)
You can't shrink your database directly from the central administration UI.
You need to use SSMS (SQL Server Management Studio) to shrink your database.
I found a nice automated solution (SQL script) to shrink all your Sharepoint related DBs: Keeping your SHarepoint 2010 Development Databases small
A different shorter method is explained here: Sharepoint: shrink database on a fast way
I think, you can't...
You need to do that in the SQL Mgmt Studio.