Note that you can (and should) be upgrading to the latest jCustomer version: either to jCustomer-1.4.4 if you want to stay on Elasticsearch 5.6, or to jCustomer 1.5.4 if you can move to Elasticsearch 7.4.
Read all of the instructions on this page carefully before proceeding with the upgrade process.
Run a pre-production test first.
Backup your jCustomer-1.4.1 instance (in case you run jCustomer in cluster, backup the whole cluster)
For a detailed description to backup jCustomer please follow the section How to backup jCustomer on this page