Update automatically a custom mini cart

I just have made a mini cart for a client's store following some suggestions at the topic Marketpress mini cart contents in menu. Everything is working fine but the only problem is that it doesn't update automatically. I know we have to add some Ajax there but I'm not experienced with that and would like to ask you the simplest way to do that, or if someone know a good resource to solve this issue quickly...
My dev website is here: Operation Pillow Pets.