Hi Fabiana.

1st step. Crop mobile logo image, must be ONLY real logo, without extra top space. Upload & Change.

2nd step. Use that Custom CSS:

@media screen and (max-width: 680px) {
#sp-logo {width: 75%;float: left;padding-right: 0;}
#sp-menu {padding-left: 0;width: 23%;float: left;}
}