What should I do about this Adsense Suggestion?

I got an email from Adsense with certain feedback of data. It also contained the following content.
" We've noticed you're currently using synchronous ad code which can potentially slow down your pages. Switching to asynchronous ad code means visitors can get to your content quicker because the ads don't get in the way of the content loading. Just copy the code from your account and paste it on your site." Unquote

I am not much in the know of these things. What am I supposed to do in this regard? If so, how to do that?