Andreas09 Add Image to Header

I have spent the last few days, and many hours, trying to learn how to edit wordpress themes, and I have never asked a question before I have been able to find it out for myself, or find the answer somewhere else, but I have searched for far too long.

I would really appreciate it if somebody would point me to a resource, or tell me the best way, for me to add an image to the Andreas09 theme’s header (I allready changed the background graphic to only show the top section and this retains the layout). I need the graphic to be in the top but also keep the stretchy graphic to fill in the extra space. I would like also to keep the Title and Description in the header or H1 text but hidden to help engine rankings without breaking the layout.

And if anybody is able I would also be so thankful if I could know how to add as many items to my header as I wish (i.e. a random qoute with a plugin).

This is the site I am having trouble with:
https://blogagloco.com/

I know this might be a large request but, thank you very much to whoever might answer this, I have been spending far too much time trying to edit my templates and far too little time posting.