how can I make GIF over a static image?

[kenny1999]

Hi all

I'd like to start with an easier example. 

Gif is already provided (I don't want to learn about creating GIF)

but then I'd like the background of the GIF replaced with another background

Example gif and image below

I'd like to replace the background of the dynamic dinosaur with another background

How to do it?

I'd like to replace the background of the following dinosaur
https://gifyu.com/image/6SoM

with this background


How to do it? Can someone highlight me the steps?

---

by the way, by the end of the original gif, when the dinosaur roars,
the background moves up to the sky. If I'd like to have the same
effect on the new background, how should I make it?