We own an AWS account but we're no longer in contact with the developer who had sole access to the running EC2 instance.
Restarting the instance may not be possible: As far as we understand, shutting down an instance can cause changes in the assigned IP. Also, there may be app processes that need to be started manually. We don't know yet.
Thus, the question: Given that we own the account and have access to the AWS admin UI, how can we gain root access to our running instance?
(All we've learned so far points to installing new keysets that will give access to NEWLY started instances.)