Official Upgrade, excerpt.
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo apt install mintupgrade
sudo reboot
sudo apt autoremove
mintupgrade check # follow instructions on error and/or
# mintupgrade restore-sources # go back to your original APT configuration
mintupgrade download # only if no more errors before
mintupgrade upgrade # point no return
# after a while there is a question for auto restart services, OK
# a few times there is asked for your password, do so
Detailed instructions:
https://linuxmint-user-guide.readthedoc ... nt-20.html