Possible duplicate of Modify twitter bootstrap navbar.
I guess this is what you are looking for (copied):
.navbar .nav,
.navbar .nav > li {
float:none;
display:inline-block;
*display:inline; /* ie7 fix */
*zoom:1; /* hasLayout ie7 trigger */
vertical-align: top;
}
.navbar-inner {
text-align:center;
}
As stated in the linked answer, you should make a new class with these properties and add it to the nav div.
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