Thanks for your steps. I modified it slightly to simplify it and to only delete CDRs older than a date. Here are the steps:
SSH to the server.
mysql
use asteriskcdrdb;
DELETE from cdr WHERE calldate < ‘2013-11-01 00:00:00’;
In the example above any CDR before Nov 1 2013 will be deleted. Change the date to whatever date you would like to use.