I had upgraded kernel of Ubuntu 12.04.2 LTS and Fedora 18 to the latest update. I had updated the Ubuntu's GRUB with command
$ sudo update-grub
When i updated the grub, I had mounted Fedora's partition. However, Fedora's GRUB2 take over bootloader.
How should i do to make Ubuntu's GRUB taking over the bootloader?
Boot into ubuntu
Add repository
Install boot repair
Then run boot-repair from terminal
This might work. At least its something to try. It should launch a gui giving you options to help you fix grub. Its quite easy to use and self explanatry
Boot into Ubuntu and run
sudo dpkg-reconfigure grub-pc
.