Upgrade path from working emonpi image

I've got a very functional Pi2 running EMONCMS V8.5 VLow Write and OPENHAB. What is the recommended upgrade path to the latest versions whilst keeping my existing data? I use MQTT to transfer data between EMONCMS and OPENHAB via EMONHUB so I need to keep the EMONTX / RFM69Pi MQTT version of EMONHUB working.

Thanks in advance