Replace the header

I appreciate there have been some questions and answers here about the piano black header, but I am real novice and therefore still stuck.

I am planning on using the piano black wp theme cuz I think it looks elegant.

I have created a jpg header that is the exact size of the default paino black header.

First what should I name it? Would “new_header.jpg” be okay?

Second where should I upload the new header to?

Third where and what should I look for in appearance in my dashboard to change the header?

Fourth what should I do to change the header?

If someone could provide me with a “piano black header change for dummies” in a step by step form I would be very appreciative.

I know this is a rather basic request. Hopefully I will know a lot more by the time I am finished this whole thing, and maybe even be able to help spme novice like me someday:)

Cheers, Ed