After upgrade from RC3 to RC4 problem with postfix

[DaSilva]

OK, thanks.
Is it enough to change to this name in /etc/hostname or do I have to write it in other places, too (e. g. /etc/hosts)?
Which services have to be restarted or must I reboot the whole system?
Thank you very much!

EDIT: Additionally I wrote "hostname s1.frefel.net" in PuTTY (SSH). What else must be changed and do I need to reboot the whole system?
Thanks

EDIT2:

/etc/hostname

s1.frefel.net

/etc/hosts

# 'hosts' file configuration.

127.0.0.1 s1.frefel.net.local localhost
193.34.68.126 s1.frefel.net frefel
::ffff:193.34.68.126 s1.frefel.net frefel
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Is this ok?