master

HTML

<script src="http://chartjs.org/dist/master/Chart.min.js"></script>
<button id="destroy">
  destroy
</button>
<button id="new">
  new
</button>
<div style="position:relative">
  <canvas id="canvas"></canvas>
</div>

JavaScript

var canvas = document.getElementById('canvas');
var def = {
  type: 'line',
  options: {
    responsive: true
  }
};
var chart = new Chart(canvas, def);

document.getElementById("destroy").addEventListener("click", function() {
  chart.destroy();
}, false);

document.getElementById("new").addEventListener("click", function() {
  chart = new Chart(canvas, def);
}, false);