guix pull only syncs the package definitions
To update the packages in your profile use
guix package -u
If you are also running GuixSD you will need to reconfigure your system (guix system reconfigure) to update your kernel.
The getting started doc describes the same process (guix upgrade is an alias to package -u), see:
https://guix.gnu.org/manual/en/html_node/Getting-Started.html