I’m upgrading from Nest Thermostat to Gen 4 Learning Thermostat

Has anyone ever upgraded? I’m assuming I need to remove the old Nest Thermostat from Google Home first? If so, where is that option? I’ve found several YT vids on installing. And have read several articles about installing. I haven’t seen or read anything about having an existing Nest Thermostat and upgrading to a Learning Thermostat.