@SKC123 Assuming you have kept the default setting of using a dynamic IP connection you really should be able to simply unplug the ethernet cable from your copper ISP's modem, maybe wait a few minutes, then reconnect the ethernet cable to your new ISP's modem.   If your new ISP installed a router you will have the choice of connecting to an ethernet port on that router, or disconnecting their router.   Once your Deco comes up on the new connection you shouldn't have to change anything else.   All devices already on your Deco network will still be on the network.   I think you can do this safely without powering down your Deco routers, but if you're nervous about that it won't hurt to power it down.  But you would only need to do that with your primary Deco, not the mesh connected ones.