migrating cores with Solr upgrade

[Piyush Kumar Nayak]

Hi,

What is the best way to migrate cores from an old version of Solr (say 5.x) to 
a newer version (say 7.x). I did not find anything pertinent to the matter in 
the Solr reference guide.
Is there a tool that can do that seamlessly?

Regards,
Piyush.