WP theme appearance doesn’t change

Hello I currently installed this theme MMOpress and when I try to edit anything in appearance mode it ends up either messing something totally unrelated to he code I am working on (for instance I tried to erase the footer links and it ended up deleting my banner) or it has no effect at all. Even if I change the background image nothing happens. I really have no clue what to do. This theme is perfect and I would really love to get it up and running the way I want it, so any help would be well appreciated. Thank you.