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)?

Membership? - **WARNING ** BEWARE** - Download p2p Clients ONLY Thru Official Sites

The official site offers Pro ($21.95, free updates & email support for 6 months), Extended Pro ($34.95, free updates & email support for 12 months) & sometimes a one-off deal where you can buy Pro for $13.95 but don't get any email support or free updates..
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 buy Pro from the official site, you recieve 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. Providing your Pro's not out of date, that link is what you use to download another Pro