Partner passed away, need to cancel his account

What do I need to do to cancel my partner’s account? He passed away a few weeks ago and said that I won’t be able to cancel it until after he’s gone and I can bring a death certificate. I don’t mind going to the nearest store to do this, I just don’t want to forget something and have to go back and forth. I already have so much to do since his passing. I’d like to get this taken care of quickly. 

thanks in advance