I do manual upgrades on my machines because I only have a few and they're different enough that automation wouldn't help, buuuut... You can use release(8) and a

I do manual upgrades on my machines because I only have a few and they're different enough that automation wouldn't help, buuuut... You can use release(8) and autoinstall(8) with pxe to deploy create and deploy OpenBSD upgrades/installs. In between releases, you can follow the -stable branch of the ports tree and use dpb(1) to generate updated binary packages, which all your machines can then install.