Switching the storage engine
In order to use a different storage engine with an existing data directory, it is required to first create a logical backup of the data using the tool arangodump.
After that, the arangod server process should be restarted with the desired storage engine selected (this can be done by setting the option --server.storage-engine, or by editing the configuartion file of the server) and using a non-existing data directory. If you have deployed using the Starter, instead of arangod you will need to run arangodb, and pass to it the option --server.storage-engine and the option --starter.data-dir to set a new data directory.
When the server is up and running with the desired storage engine, the data can be re-imported using the tool arangorestore.