The OpenBSD Upgrade Guide: 7.5 to 7.6 at [0] links to the sysupgrade(8)
man page. Following that link returns an error page for a bad request.

Broken link is:
<a href="https://man.openbsd.org/OpenBSD-7.6/sysupgrade.8">sysupgrade(8)</a>.

[0]: https://www.openbsd.org/faq/upgrade76.html