As I know, you can do some multiple file actions in the right window (In the left window you can select only one file). Select multiple files and then you can start the context menu (right mouse click), delete theme all or edit some attributes.
As far as I found out, there is no multiple add or replace option possible. Add or replace can be only done for one file ....
If you miss the option in the context menu, goto the Options menu and activate the last point in the third tab.