Adding Image Header to Modern Clix theme

Hey guys am a totally newbie to the whole coding thing, started with a wordpress blog but then bought a domain and learnt some basic stuff online to get my website up and running, which u can view here:

https://www.prioryofzion.co.uk

i would like to add an image to the header section at the top which looks a bit bare, retaining the text with the image behind it, further more would it be possible to have a selection of images, which could be rotated through?

thanks for any help.