To get up-to-speed with using Enterprise Developer to edit and maintain your mainframe applications, check the Getting Started book in the help and, more specifically, the Mainframe tutorials. Start with the tutorial "Getting Started with Enterprise Developer" which provides basic understanding of how the product operates. Move on to the other tutorials which provide details about developing CICS, JCL and IMS applications.
If you consider upgrading your development environment to Enterprise Developer, you can contact Micro Focus' Technical Services for assistance. They have a utility that automatically converts Mainframe Express projects to Enterprise Developer ones.
In addition, please note: