I wish someone could have told me that when I was an intern. Many times.
If the upgrade blows up, it won't be your fault because you're just an intern. There are multiple people making way more money than you are who are responsible for running the company. If those people leave an intern in charge of a mission-critical system and it breaks, it's their fault. If you do end up in the soup and you're able to save the day by calling Epicor support, you'll end up with some very nice letters of reference.
If it doesn't blow up, great, it means your advisor trusts you to keep the plates spinning while he's out. Keep doing what you're doing and you'll have a bright future.
Next time get trained before the guy with the knowledge disappears :)