there isn't an official procedure for that, but it is possible. things to solved :
a) getting zabbix updated. theoretically, you could try to grab zabbix packages from a latter package... but there is no appliance for rc2 ;)
you can either build your own packages or just remove the packages zabbix from the appliance and install from the source.
b) patching the database
database has changed a bit, and there are no official patches. there are unofficial patches, but only for mysql. luckily, appliance is using mysql.
you will have to dive into https://zabbix.org/wiki/How_to/trunk_db_patches
and see which method you would prefer, then figure out how to use it. database backup is _highly_ suggested.
detailed questions on this might fit in irc quite well :)