How to fix grub after upgrading Macbook pro - reinstalling grub

Followed the last step in this post: 

Mac Pro cannot boot

Press Alt while restarting the system with the USB drive inserted. The USB should contain a Ubuntu system.

Run boot-repair by logging into Ubuntu (using a USB if the installed version is broken). After running the fix, I have to use the GRUB menu to start the windows, not the original Alt + Power and select Windows way.

https://help.ubuntu.com/community/Boot-Repair