use this CSS for the center a menu, and this css on your additional css
.menu-primary-container{
text-align:center;
display: inline-block;
width: 80%;
}
.main-nav >li {
float:none!important;
display: inline-block!important;
}
.top-header-socialicon {
display: inline-block;
}
for your logo, you need to go to customize > site identity > upload your custom logo or brand logo
Thank you