Hi,
What would be the best way to migrate all my User and Roles from a cluster running 6.8.0 to a new cluster running 7.5?
If you are upgrading from 6.8 to 7.5, you should follow the various steps in the upgrade guide.
If you are trying to copy roles from one Elasticsearch cluster to another, that is probably a question for the Elasticsearch forums. Kibana roles are a superset of Elasticsearch roles, so they are permissioned the same way. Here are the APIs you can use for managing security: https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api.html