Check the Release bulletins at http://sybooks.sybase.com/as.html.
You can also find installation, migration, and what's new
documentation.

The drifference between upgrade and migration to me is
upgrade - databaserver stays the same and is started using a new
software release which may cause data modifications.
migration - a new dataserver is created using the new software
release and the data moved from the old server to the new.