To upgrade Guix, run:
guix pull
See Invoking guix pull, for more information.
On a foreign distro, you can upgrade the build daemon by running:
sudo -i guix pull
followed by (assuming your distro uses the systemd service management tool):
systemctl restart guix-daemon.service
On Guix System, upgrading the daemon is achieved by reconfiguring the system
(see guix system reconfigure).