I would expect more packages than just the one, given that your original post contains reference to package like linux64-nvidia.
In any case you have only this EOL kernel installed and running.
You will need another.
sudo mhwd-kernel -i linux61
It may fail due to your current state.
If so try again with:
sudo pacman -S linux61
If you can successfully install another kernel then you want to reboot into it.
Make your selection at Grub, and verify your running kernel with
uname -a
Once you are surely in a different kernel you can proceed with removing 64;
sudo mhwd-kernel -r linux64
(and/or check again with pacman for more: pacman -Qs linux64)
Once all of 64 is removed you should be able to continue your updates:
sudo pacman -Syu
And reinstall your drivers for good measure;
sudo mhwd -f -i pci video-nvidia
(or whatever your driver profile is).
If for whatever reason you do encounter an unbootable system then see this: