Hello @UtilityHawk,
to update to KNIME version 4.2.0 new installation was needed (see here) so would say going from 4.0 to 4.3 is not possible. As @mlauber71 said you need fresh installation. Point your new workspace to old location and your workflows together with preferences should be the intact. Only thing left is to install extensions you had.
Anyways just to say in case you are not doing it or doing it irregularly that it is suggested to do workspace backup on regular basis…
Br,
Ivan