Raising Bridge to play slide

I am wondering if there is an instruction on how to raise a guitar's bridge in order to raise the strings to play slide guitar. Anders mentions wood blocks under the strings to raise the strings in one of his lessons. Can anyone tell me the easiest way to do this. I know I can take it to the guitar shop but if it is something I should know how to do, I would like to know how. Thanks.

I bought one of these (shown in the video) at my local music store a few years ago.
http://www.guitartricks.com/lesson.php?input=12321

Thanks. I had seen that once before but forgot about it. I will give it a try.