Newbie: install went fine; now I can’t add a picture to my customizable header

Hi. I’m brand new to WordPress and have very little knowledge of all the “basics” but I read everything I could find on my topic on the forum and support pages, I promise!

I am hosted by 1 and 1. Created the myslq 5 database, uploaded wp with filezilla to the database, installation went fine as far as I can tell. I added a new theme (WebMinimalist 200901) and added my posts and categories and used my widgets. Yea! But when I go to add my image to the “customizable header,” I go through all the motions, select it from my computer, click “upload” and … nothing. Blank screen comes up and when I go to my site, it still has that damn palm tree on it. I even downloaded another theme that had the nifty “add a picture to your header” feature and it did the same thing.

Can this be a 1 and 1 thing? And can it be fixed? And, if you know the answer, can you please explain it like you were explaining it to your grandma? That’s about how much I know about all this … and just about how old I am.

Thanks in advance!

Julie

My site is https://www.moderndaymiddleage.com