...
var ctx = document.getElementById("chart").getContext("2d");
var myChart = new Chart(ctx).Bar(data);

myChart.destroy();

myChart = new Chart(ctx).Bar(newData);

data.labels = [5, 6, 7, 8, 9];
data.datasets[0].data = [5, 6, 7, 8, 9];
myChart.destroy();
myChart = new Chart(ctx).Bar(data);