Well by looking at their site, the latest Version is 4.18.8. What Version do you have ??
Try going to your Pro Support Page and click on Upgrade. I think this will take you to where you can Enter the E-Mail Address that you entered when you First Bought Pro. Once e/m Addy is Added, you should be able to get the Upgrade.
I haven't used LW for quite a long time so I'm going off of Memory. Seems that's what worked for me.
Just wondering...What site did you Buy Pro from ???