You will find a section in the AS documentation. But migrating an EJB2 application will be more difficult than EJB3.
It might be an option to migrate to EJB3 in the same step, that depend on the application size and complexity.
As it might happen that you have to change the code additional to all the XML stuff.
If you have EJB2 Entities you should consider that this is marked as 'optional' in JavaEE7 and will be removed in WildFly (former known as JBoss AS8).
Do you use XDoclet to generate the DD or do you write it by hand?
If you have specific questions you might as here in the forum.