If you're asking how to update ports/packages in OpenBSD, there isn't an official way to do that anymore.. the -STABLE ports tree was removed and is no longer maintained.
Lack of man power led to this.. it's unfortunate, but that's the state of things.
If you're asking how to apply errata patches to the base system, this is documented on the FAQ.
http://www.openbsd.org/faq/faq5.html
http://www.openbsd.org/errata44.html