Make sure there's no other Subsonic process running (look for java processes and kill them). The error says that another process is indeed running and has locked the Subsonic internal database file, so when you're starting a new process, it can't access the database and fails.
I don't know how your previous install is set up, but basically, you need to replace the two java archive files (subsonic.war and subsonic-booter-with-dependencies.jar) in your current installation with the ones from the zip file on the MusicCabinet installation page and then start the Subsonic process just as usual.
The settings from your 4.7 install will be read and transformed into MusicCabinet 0.7 format (for example, updating passwords to be stored as salted hash sums instead of clear text). That's why it tells you to make a backup of your current settings before installation, as you can't go back from MusicCabinet 0.7 to Subsonic 4.x unless you save your current settings somewhere.