Janus Notes 2 requires OS 10.9 or later on Macintosh and iOS 7 or later on iPhone/iPad. If you don’t meet the minimum requirements, simply stay with Janus Notes “1”. It will happily continue to sync through dropbox as before.
To migrate you need a Macintosh with both Janus Notes and Janus Notes 2 installed.
From the Janus Notes menu select “Upgrade To Janus Notes 2”. Save a notes archive from Janus Notes, install Janus Notes 2 and, from the latter, Select File --> “Restore Notes Archive” and select the archive you just saved.
Your notes will be in the new platform.