If you still know the email address that you registered on your LFS account, then you should be able to quickly retrieve your account details.
In the event that you do not have access to that email address anymore, then the only way to gain access to your account again is to provide proof of purchase for the license you bought. Something like a scan of a credit card statement with an entry for WWW.LIVEFORSPEED.NET or a PayPal transaction ID will do.
If you also do not have access to such information then unfortunately we cannot help you gain access to your LFS account. This is for security reasons but also in the end you are the one who is responsible for your own account details.