The BIND 9 distribution, and the prepackaged versions too, contains
a document called migration that contains notes about how to
migrate from BIND 8 to BIND 9. The document is very straight forward.
If you installed binary packages it's likely stored in
/usr/share/doc/bind* or /usr/doc/bind* somewhere.
If you're running BIND 4, you may find a document called
migration-4to9 in the same place.