After loading 4.5.6 and it finishes loading, go to your lib/ folder and locate h2.jar.
Right click -> open with -> Java(TM)
It will load up your browser with it's built in SQL database manager.
In JDBC Url use the relative path to your plugins folder: ../plugins/iConomy/[database name] (Usually minecraft)

Example:
Code:
jdbc:h2:../plugins/iConomy/minecraft
Username: sa
Password: sa

Connect, now you can access the database and it's information.

SQLite Export
Use SQLite database browser or something similiar (google if you can't find one), open your minecraft.sqlite or whatever it is named from your plugins/iConomy/ folder, export your data from iConomy and only copy the [INSERT INTO] queries / lines.

Paste that information into the box on the first page you land on when you click the button that says Run(CTRL+Enter)

And that should be that!