How long ago did you buy Pro?
Did you buy Pro from the official site? Lime Wire » Download LimeWire
Did you pay LimeWireLLC for Pro (check your CC statement)?

Did you buy Pro for a year or 6 months? Your email address will only be recognised in the official database while your Pro's current - if you bought Pro for 6 months, your email address stays in the database for 6 months, if you bought Pro for a year then your email address stays in the database for a year. After that, your email address is removed from the database & you can't download free updates any more.

If you paid a scam site for Pro then you won't ever be able to update from the official site.

After you bought Pro, you would have got an email from LW with a link to your Pro personal download page. Have a look through your emails & see if you can find it. If you bought from the official site, LW will send you an email telling you when your Pro's about to expire