You will need to visit your PC manufacturer's website and check the stautus of their upgrade program. From there you will be able to tell if you qualify for a free upgrade to Windows 7. Be sure to have your reciept handy too.

*Upon re-reading your question after posting, I noticed you said 2008. Did you mean to say 2009? If it was in-fact purchased in 2008 it does not qualify for a free upgrade to Windows 7.*