Hypar Space now makes it easier to work on multiple floors at a time.
Use the views menu
If you have a function that produces levels (e.g. Levels By Envelope, Simple Levels by Envelope, Levels by masterplan), then you can access the associated view by going to the view menu in the view toolbar:
Select the Level Volume
You can also select a level volume directly, and navigate to its associated plan view by clicking its "scope" button in the tooltip:
Use Element Relationships
If you're not sure the name of the level you want to access, or the level is not visible, you can click on an element on that level, like a floor or a space boundary, and use that to focus on the associated plan view: