A good place to start would be your log files. See which pages (files) are being visited the most, since these are the files that would probably contain any code that needs tweaking. If your server is too busy, you can check these things to see where the problems may lie:
1. The software you use to display content - PHP, HTML, mySQL...
(The software may be taking too long to process the huge number of requests your web server is receiving. Check their configuration, and also make sure you don't have other processes running that are wasting memory and cpu usage)
2. Or you could have everything working just fine, but but may need to upgrade your servers. Dedicated is always a good way to go. Beyond that, I think you would need to do some DNS redirecting in your server to redirect traffic to other servers you own..
hope that helps