In Concept Mode, a droplist allowing you to choose the level you are viewing has been added to the toolbar at the top of Plan View.
Previously, the only way of doing this is by going to the Floor and Roof Levels dialog, accessed from the toolbar, and the only way of knowing the level you are on is through the status bar at the bottom right corner.
Version 1 of the software allowed users to change levels from a menu item, which is a bit faster than the dialog, but this was dropped for version 2. This restores this functionality, if somewhat belatedly, for version 9.