Hi there,
it looks like you installed the Navigator Site which adds a fixed side header.
To remove that go to Customizer > Additional CSS and delete:
/* ------
Fixed Header
------- */
@media (min-width: 769px) {
body {
margin-left: 200px;
}
.site-header {
position: fixed;
left: 0;
top: 0;
width: 200px;
z-index: 300;
height: 100%;
overflow: auto;
overflow-x: hidden;
-webkit-backface-visibility: hidden;
-webkit-overflow-scrolling: touch;
transition: .1s ease;
}
.admin-bar .site-header {
top: 32px;
}
.site-header .main-navigation li {
float: none;
}
}
.inside-header {
display: -webkit-box;
display: -ms-flexbox;
display: flex;
-webkit-box-flex: 1;
-ms-flex: 1;
flex: 1;
-webkit-box-orient: vertical;
-webkit-box-direction: normal;
-ms-flex-direction: column;
flex-direction: column;
-webkit-box-align: center;
-ms-flex-align: center;
align-items: center;
height: 100%;
-webkit-box-sizing: border-box;
box-sizing: border-box;
}
.site-branding,
.site-logo {
-webkit-box-ordinal-group: 2;
-ms-flex-order: 1;
order: 1;
}
.header-widget {
-webkit-box-ordinal-group: 4;
-ms-flex-order: 3;
order: 3;
margin-top: auto;
margin-bottom: 20px;
}
.nav-float-right .inside-header .main-navigation {
-webkit-box-ordinal-group: 3;
-ms-flex-order: 2;
order: 2;
float: none;
margin-top: 20px;
margin-bottom: 50px;
}
.nav-float-right .header-widget {
float: none;
top: auto;
max-width: 100%;
}
.dropdown-hover .site-header .main-navigation .main-nav .sub-menu {
opacity: 1 !important;
display: block !important;
right: auto !important;
position: relative;
top: auto;
float: none;
text-align: center;
}
Then i suggest you go to Customizer > Layout > Header and enable Navigation as Header.