These are the sources I used:
Hope these help!
Yeah, this answer has definitely changed in the past year and a half. I know that they "archived" their user training from Atlassian University in a YouTube playlist - here's the link for that.
As for the administrator training, I haven't been able to find that anywhere.
I think that you should start with Atlassian University.
Moreover, I would follow the questions being raised here in Atlassian Answers (you can watch tags like jira-administration, for example). So each new question that has this tag will send you an email. You can of course go over older questions too. Most of the day-2-day questions were already asked in the past, so you should find what you are looking for.
And of course, Atlassian has a good knowledge base - look at the middle column titled Administer JIRA.
Most of the information is easily available on the internet and on Atlassian official website but if you are looking for a single guide then books by experts can really be helpful and you would find everything in one place. It is difficult to find one book that suffice all your needs. The books referred above are by experts and I also recommend them.
I would like to mention that I wrote Mastering JIRA last year and it has information about customizing and administring JIRA.
I will plug my own resources, as it matches your criteria (it is FREE and up to date)
I have Youtube videos that cover different parts of Jira, I am sure you will benefit from it. I myself worked with Jira for many years as a Developer, Manager, Scrum Master.
Here is one of the videos, on Jira UI:
Hey admins! I’m Dave, Principal Product Manager here at Atlassian working on our cloud platform and security products. Cloud security is a moving target. As you adopt more products, employees consta...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs