You just need to bind a variable into the directive "ng-class" and change it from the controller. Here is an example of how to do this:
var app = angular.module("ap",[]);
app.controller("con",function($scope){
$scope.class = "red";
$scope.changeClass = function(){
if ($scope.class === "red")
$scope.class = "blue";
else
$scope.class = "red";
};
});
.red{
color:red;
}
.blue{
color:blue;
}
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<body ng-app="ap" ng-controller="con">
<div ng-class="class">{{class}}</div>
<button ng-click="changeClass()">Change Class</button>
</body>
Here is the example working on jsFiddle