Many thanks for the information. It says this on the trial version -
Installing the trial version will overwrite your existing Melodyne plug-ins. This is technically unavoidable, unfortunately, because for reasons of compatibility the Melodyne 5 plug-ins use the same plug-in ID and can therefore not be operated in parallel. The new trial version, however, will not affect your license or the stand-alone implementation of your existing Melodyne.
'When you have finished using the Melodyne 5 trial version, you can simply download from your user account the installation program for your previous Melodyne and reinstall it, thereby restoring your existing working environment.'
Do I understand it to mean that if I download the trial version , any melodyne edits I've made in older tracks will be lost? But then if I purchase version 5 I can download the old version too and things will be restored or can't 4 and 5 be on the same computer?