You can execute those commands in a TTY:
Cntrl-ALT-F3 or F4 etc., login and execute those commands.
From my notes regarding updating after a long time:
In TTY:
sudo rm -R /etc/pacman.d/gnupg/
sudo rm -R /root/.gnupg/
sudo pacman-mirrors -f5
sudo pacman -Syy gnupg archlinux-keyring manjaro-keyring
sudo pacman-key --init && pacman-key --populate archlinux manjaro
sudo pacman-key --refresh-keys
sudo pacman -Syyu
Good Luck