There is currently no upgrade path directly from Cement 2. Cement 3 is the first iteration of a new/modified codebase and as such breakage was intentionally not a concern.
In general, usage is very similar. However, paths to classes and class names may have changed and will need to be modified. If not married to your existing application layout/design/etc, it would be recommended to start a new project using the
cement generate developer tools, and move code into it piece by piece.
Data Folk Labs, LLC (the creators of Cement) do offer consulting and development services, and could evaluate the migration of a Cement 2 app over to Cement 3. Please contact us if that is something you'd be interested to inquire about: firstname.lastname@example.org.