PhyMyAdmin in your cPanel has a tool that allows you to optimize tables. Running this command will in essence defragment the table. Generally you don't need to use it unless you have a table this is often inserted, updated and deleted.

To optimize a datbase:

1. Log into phpMyAdmin
2. Choose your desired database by clicking on it in the left menu
3. Under the "Structure" tab, click "Check All"
4. Next to the above link is a drop down menu, select Optimize Table from this drop down list.

If you're looking for more information on the Optimize Tables command, please see the official documentation for use of the Optimize Tables command.