You can try https://central.owncloud.org/t/copy-files-from-owncloud-to-owncloud/13194/2?u=jvillafanez
The only problem I see with your case is that you'll likely need to sync everything again from the new server. This might not be a big deal for mobile clients because they just sync metadata on demand, but the desktop client will need to download all the files again.
You can try to move the files to the new server using the desktop client, so basically you'll be uploading the files from your computer to the new server, but note that if you have more desktop clients connected from other computers, the rest will sync all the files.
Depending on the amount of data you have and your setup, I might still recommend to upgrade instead of using a new installation.
In any case, make sure you know what you're doing and always have a backup. Note that moving data between different servers like what is proposed is untested and might have more drawbacks than the ones explained above.