No need to repurchase. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest.
If you have lost the install file, all release installers are available here. Grab the latest from within the six-month window and register it.
If the registration has been lost, go here and click on the appropriate link.
If problems arise come back here.