To update Kali, first ensure that /etc/apt/sources.list is properly populated:

cat /etc/apt/sources.list
# See https://www.kali.org/docs/general-use/kali-linux-sources-list-repositories/
deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware
# Additional line for source packages
# deb-src http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware

After that you can run the following commands which will upgrade to the latest Kali version:

sudo apt update
sudo apt full-upgrade -y