We all know the "Switch to UI15" button in the personal preferences' dialog, which allows the nostalgic among us to go back a few years in ServiceNow's UI evolution:

And wouldn't it be great to have another button in the same place to jump to the next stage of the UI evolution called "Next Experience"? And indeed there is such a button "Enable Unified Navigation" and no, this is not an image montage:

The prerequisite for this is, of course, that your instance has the San Diego release. But then the only configuration to be done is setting the system property glide.ui.polaris.on_off_user_pref_enabled to "true".

Having activated the "Next Experience" you can find a corresponding switch in the Display preferences: