Beginning with FreeBSD 6.2-RELEASE, binary upgrades between RELEASE versions (and snapshots of the various security branches) are supported using the freebsd-update(8) utility. The binary upgrade procedure will update unmodified userland utilities, as well as an unmodified GENERIC kernel, distributed as a part of an official FreeBSD release. The freebsd-update(8) utility requires that the host being upgraded have Internet connectivity.

Source-based upgrades (those based on recompiling the FreeBSD base system from source code) from previous versions are supported using to the instructions in /usr/src/UPDATING.

For more specific information about upgrading instructions, see http://www.FreeBSD.org/releases/9.1R/installation.html.

FreeBSD 9.0 and later have several incompatibilities in system configuration which you might want to know before upgrading your system. Please read this section and the Upgrading Section in 9.0-RELEASE Release Notes carefully before submitting a problem report and/or posting a question to the FreeBSD mailing lists.