If all you want to do is to change the default boot entry in Grub2, you just need to edit the /etc/default/grub file. The beginning of that file is shown below:
# If you change this file, run 'update-grub' afterwards to update
There are also files in /etc/grub.d where you can make changes. I have Ubuntu 10.10 installed and at the top of the /boot/grub/grub.cf file is this line:
That boots the first menuentry so you could count down to whichever entry to put the number you want, counting from zero. My experience with editing grub.cfg is that if I run update-grub after editing it and don't have the changes in one of the other grub files in /etc, the changes disappear.
I'm not really clear on your situation. If you have windows and Fedora, why don't you just boot Fedora and make the changes? Are you not able to boot Fedora?