Re: How to switch an enterprise gateway?

 In power bi service click on Settings icon (wheel) on top right hand corner -> Manage gateways -> Remove your old gateway from the list. Then go to your dataset settings and provided you have added data source under new gateway you will have an option to choose this new gateway (as old is removed by you).

Alternatively old gateway from service, remove your report (if not shared with anyone currently), then re-publish your report and it will use your new gateway (provided old gateway is removed, new one has data source added).