do i need to use Kibana for upgrading? I dont use this instance with Kibana.
Yes, the Upgrade Assistant is part of X-Pack for Kibana 5.6. Please ensure you've installed this into your Kibana instance, or else the upgrade assistant won't appear in the Management app.
what i now tried is creating each index new. After that i set up my analyzer and mappings with elasticdump and reindexed all indices with _reindex. Is that correct?
That is a valid alternative for upgrading. You can use the Reindex API to transfer index data from a remote Elasticsearch instance. This can also be used when the mapping has been changed. As you found out already, the Reindex API requires you to set up mappings for your new indices before ingesting any data, as otherwise the default mappings are being used. Comprehensive details about breaking changes are available in the documentation, but it largely boils down to converting any
string fields to either
Therefore you should review your index mapping and create a version compatible with 5.x and 6.x (pay attention to not using multiple document types!), before upgrading.