Pushing the onstar button in the car would be a good place to start. Have them link the ELR to your existing account and inform the CSR that you no longer have the '15 Volt which should remove that from your onstar app. As for any upselling, My suggestion is to just be firm from the get go and tell them you are only interested in whatever package came with the car at purchase. When I set my '13 up I did have them try to upsell, but I was firm in that I was only interested in the 3 free months of full service, and the balance of 3 years of "free" service.