Showing and refreshing advertisement

I want to show an advertisement in my application, and after some time I want to refresh it and show another advertisement. How can I do this? Please help me give some sample code.

I am new to iPhone programming. Thanks in advance.

Use NSTimer. In the Firemethod you can change UIImageview's image.you can maintain flag variable in that method.suppose the firemethod is called every one second, the flag variable will be incremented, it it equals to 5, show one image, if it equals to 10, you can show another image.reset flag variable in after showing last image..