1. In your administration panel click Personalization and then Header.
2. Find an option “Choose an image” or something that sounds like that (I don’t know this option’s real name because of my Polish version of WordPress ??
3. Click “Browse” and upload the image you want on the server
4. WordPress may like you to cut it to fit the page, but in Arcade Basic I think it isn’t required.
5. Enjoy!
Hope my answer was helpful ??
I also use the Arcade Basic theme and I am relly satisfied with it. If you want to check my WordPress website, it is here https://marta.hekko.pl/ (I haven’t created english translation yet, but if you only want to see the layout it will be ok).