sail - backup the database (it's at /opt/sark/db/sark.db) then just download the latest rpms (sail and smesailenv) and install them with yum localinstall. Then do:-
signal-event post-upgrade; signal-event reboot
Should be all good to go.
The iso is just an augmented sme iso. You should be able to yum upgrade it in the normal way but Asterisk will almost certainly break due to kernel dependencies. If that happens you'll need to find suitable DAHDI kmdls for the new kernel or boot with the old kernel. In general, we don't tend to yum upgrade Asterisk systems unless they are already in some distress but as long as you have time to hunt down the kmdls it should be OK. To be on the safe side, you might want to rehearse the upgrade on a test VM before you do it on your live box.
Kind Regards
S