I don't know that I have all the answers, but I'll start with some basics.
If you're wanting to update/edit his profile, you'd want to first set up an account and become confirmed as a Volunteer, so that you can edit profiles. It's not a complicated process and there is no cost to join.
Once you've got an account, you would need to work with the current profile manager to be added to the trusted list. It is possible that the manager may even want to transfer ownership of the profile to you, since you are a direct descendant.
I think that covers the highlights, but others may want to chime in and add additional details that will help you on your way.