To update Bastion, first of all, you will need to navigate into the Bastion directory. That is where the script is!
cd ~/Bastion
Then, it is as simple as running this:
./bastion.sh --update
Wait for a few moments, so that it can update Bastion and its dependencies that you need to run Bastion smoothly. Meanwhile, you can go grab a cup of coffee (or tea, if you prefer that).
Once it is done, it will let you know.
Now, you can start Bastion, as usual, simply by running:
./bastion.sh --start