Hi Heidi,
To make site logo and main navigation to be centered and main menu to be below the logo go to Appearance -> Customize -> Ambition Theme Options -> Custom CSS and paste the below CSS code then click on Save button.
@media only screen and (min-width: 768px) {
.hgroup-wrap {
text-align: center;
}
#site-logo {
float: none;
margin: 0 auto;
padding: 19px 0 0;
}
#site-title {
float: none;
margin-right: 0;
}
.hgroup-right {
float: none;
min-width: inherit;
padding-right: 0;
}
.main-navigation {
float: none;
}
.main-navigation li {
display: inline-block;
float: none;
}
.main-navigation ul li ul li {
display: block;
text-align: left;
}
}
Thank you!