After reboot, run sysmerge
In general: Read the FAQ! Updated for each release, and always available at http://www.openbsd.org/faq/
Also: Read the man pages! All commands have one (and most configuration files too!).
Upgrading? Read the upgrade FAQ! Updated for each release (and incrementally for -current), the 5.6 one is at http://www.openbsd.org/faq/upgrade56.html
More specifics -