Sorry you can not remove or switch the primary person listed.
Removing a spouse is not recommended
So sorry for your loss. For 2018 you could file a joint return. But for 2019 you will be filing as Single. If you try to use the same account and user ID and transfer that joint return to your 2019 return, you will have problems. It is too hard to remove all the information from a joint return when you change your filing status to Single. You would likely experience frustrating "errors" as you try to file.