Trouble Editing a Pre-existing WordPress Site

I’m a college freshman who recently joined a fraternity and was asked to take over as their webmaster, given my experience doing web design on internships and in my free time. Their site was made in WordPress which I have no experience working on, so I began looking up tutorials, to learn my way around, but the menu for the admin account they gave me does not look like any of the tutorials I’ve seen for 4.1.1. I do not see an appearance or plugin tab and when I try to update, I’m prompted to contact my administrator, which is me… If anyone could let me know what I need to do to update the appearance of their site through WordPress, or how I can gain access to the code, that would be greatly appreciated.