How to make logo appear bigger?

I’ve centralised mine at the top and made the bar full lenght this way:

.navbar-wrapper .brand {width:100%;display:block;}
.navbar-wrapper .navbar {width:100%;float:right;}
.header-spacer {
height: 10px !important;
}

You can play with the values to fit your needs.
Watch out for the smaller screen sizes because some values don’t respond well.

Thanks!

Do you also know how to center the text in the header and center the header itself?

Try these:

/* Remove white boxes/shadows */
.navbar .navbar-inner {
background:   	none;
box-shadow:   	none;
}

/* Hide logo */
.navbar-wrapper .brand {
display:		none;
}

/* center logo */
.navbar-wrapper .brand {
display:		block;
width:			100%;
}

.navbar {
display:		block;
width:			100%;
}

/* Hide social icons */
.navbar-inner .social-block {
display:		none;
}

/* Center social icons */
.navbar-inner .social-block {
display:		block;
float:			left;
width:			50%;
margin-left: 	50% !important;
}

/* Hide tagline */
.span7.inside.site-description {
display:		none;
}

/* Center tagline */
.span7.inside.site-description {
display:		block;
float:			left;
margin-left:	20%;
margin-top: 	0px;
}

/* Center Navbar */
.navbar .nav {
margin-left: 	50%;
}

Thanks!!