He'll need to go to his DNA Homepage and click on the little gear icon labelled "Settings". On the Settings page, right side, midway down the page he'll see an option to "Download your raw DNA data". Clicking the "Get started" button starts the process.
Once he has his raw data downloaded he'll need to go to
www.gedmatch.com, create an account, and follow the instructions from there. I was on the GEDmatch site earlier today and there's a notice posted about there being problems with registering new accounts so he'll probably need to wait till later in the week to give it a try.