Actually that’s the install one. Here’s the upgrade one:

function upg {
  exists() {
    command -v "$1" >/dev/null 2>&1
  }

  if exists dnf; then #Fedora
    sudo dnf update && sudo dnf -y upgrade && sudo dnf -y autoremove
  elif exists apt; then #Debian
    sudo apt update && sudo apt full-upgrade -y
  elif exists apk; then #Alpine
    apk -U upgrade
  elif exists emerge; then #Gentoo
    sudo emerge --ask --verbose --update --deep --newuse @world && sudo emerge --ask --verbose --depclean
  elif exists zypper; then #Suse
    sudo zypper ref && sudo zypper update
  elif exists pacman; then #Arch
    pacman -Syu
  elif exists brew; then #MacOS
    brew update && brew upgrade
  else
    echo "Error: cannot update packages. No package manager is detected."
    exit 1;
  fi

  if exists snap; then #Snaps
    sudo snap refresh
  fi
  if exists flatpak; then #Flatpak
    flatpak update -y
  fi
}