Once a release engineering team put out a new release (7.1 for example), it's handed over to the security team. They do not release new version, they fix the holes in the release versions (FreeBSD 7.1-RELEASE). Only security related issues are fixed in these releases and as ale mentioned, you just csup your sources and act accordingly to the advisories. You may alternatively fetch the patches and apply in the source directory, but csup is fine also. Once you rebuild your kernel, `uname -a` will show something like 7.1-RELEASE-p1. Always follow the procedures listed along with the security advisories.