vBulletin will probably not contact you about that, I also doubt your contact information is bound to the license so...
Anyway, you don't have to renew your license if you are using the latest vBulletin version and don't care about any possible future security patches.
If you do want to renew the license, I'd say your best bet is to place a new order for vBulletin 5 at
https://www.vbulletin.com/en/overview/, which automatically gives you access to vBulletin 4 and 3.