Hello, Hope this helps!
At the top go to galleries..once your there under the heading Photo galleries click where it reads upload picture. Once it's open you will have a "album space" which allows you to choose where you want your picture to be posted (by theme) Then there is a "picture" place. Click browse and it will allow you to add the picture you want. "picture title" (speaks for itself) same for "picture description".
When you done click upload picture. It depends on what your internet is running on to determine the amount of time it will take to upload. So it may take a few seconds give or take a few.
This should do it! Good luck