2 backgrounds, how to delete one?

New here please help!

Before I used own foto, I tried some give fotos.  Then I used an own foto for background, this was taken but  it seems ON another a little bit bigger foto of a background , so that it seems in full screen presentation that my presentation has a frame with some cactus 🙂

Two questions;:

-how can I delete the back foto?

- or, alternatively, how can I enlarge my foto u o to t he boarders?

Thank  you very much for help!