Upgrade Thingworx 8.5 to 9.4

Upgrading TWX foundation server 8.5 to 9.4 hosted customer by PTC Cloud Services.
We have following two approaches,
1. Install a fresh instance on the PTC cloud and upgrade 8.5 to 9.4
2. Upgrade existing Dev environment on PTC cloud and upgrade 8.5 to 9.4
In the existing environment, IOT devices are connected with thingworx.
Which approach is good for upgrade?