Hello,

As an important note, I always recommend taking a snapshot of your Droplet before doing a release upgrade in case that anything goes wrong.

Once you’ve done that you could try running the following commands in order to update your apt version:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get -f install
sudo apt-get -y install apt
sudo do-release-upgrade

Hope that this helps!
Regards,
Bobby