Right click on the collection and select Properties. You should be able to edit the password there.
There is an intermittent problem which I have never pinned down where editing doesn't work ( none of the buttons do anything and there is no Status: line.
To add to Jim's comment, keep in mind that ver. 18.104.22.168 sounds like an early adopter version of 4.0. At the least, you should upgrade to the production 4.0.3 release to make sure you get past any bugs present in those preliminary versions.
How to edit an existing connection password saved in SQL Developer? ver. 22.214.171.124. Currently if I want to correct a connection profile with a different password than the one saved in the connection profile, I have to delete the connection, and recreate it with the new password.
Why not just connect and then change the password using ALTER USER?
You shouldn't 'edit' a password without testing it anyway and testing it means connecting.