Adding an image under banner


I am trying to put an image in the space between my menu/title bar and my content, like a banner (dimensions not known yet).
How can I do that?
I’ve attached a screenshot of what I’d like our site to look like (
Please now that this is a university account and therefore I do not have accecss to any .php files since I do not work with IT, only in an engineering lab.

Thanks you!!!

Hey there

So I guess this is an example: and can you show me your website? please provide url.
In general, this can be done by adding an image at the top of the content