How can I save a file as a previous version?

I have 2010 version of solidworks but my friend has 2009 version,he can not open my files. how can I save my models and open them with his version?
I have 2010 version of solidworks but my friend has 2009 version,he can not open my files. how can I save my models and open them with his version?
If you don't receive the email within an hour (and you've checked your Spam folder), email us as confirmation@grabcad.com