You can also install zorin lite desktop on Zorin Core
sudo apt install zorin-os-lite-desktop
then you don’t need to make a fresh installation and you can choose the desktop at login, but to me it seems that made less problems in Zorin 17 than 18. I would prefer a fresh install if you are sure you want to stay with Zorin lite.
If you want to try the installation of zorin-os-desktop-lite on Zorin Core, it may help to install the app mending wall before. But other users have had better experiences with that app than I have.