<button id="vis1">vis 1</button>
<button id="vis2">vis 2</button>

var vis1url = "http://account.cartodb.com/yourvis1.json";
var vis2url = "http://account.cartodb.com/yourvis2.json";

$(document).ready(function(){
    $('button#vis1').on('click', function(){
        $('#map').empty();
        cartodb.createVis('map', vis1url);
    });

    $('button#vis2').on('click', function(){
        $('#map').empty();
        cartodb.createVis('map', vis2url);
    })
});