We store the application settings PER user. So find where your OS stores files for your OS user.
They are stored HERE on Macs and *NIX ($HOME\.sqldeveloper):
Find the directory that corresponds with the version you are running and having problems with. Rename it. Restart SQL Developer – you should be running ‘stock, out of the box.’
This can also come in handy any time the application hangs on a start-up or starts to act weird.
Or if you want to copy settings around, here’s where you’ll find them.
You can also find your SQL History – we store them per User, not per version.