On Fedora, to run a GUI app as root requires you to install the 'beesu' package:
su -c "yum install beesu"
beesu gedit /etc/default/grub
Or, if you're familiar with nano, simply:
su -c "nano /etc/default/grub"
Now, there are several ways of setting the Windows 7 menuentry item as the default. Check the position of the Windows 7 entry within the GRUB menu with the first entry starting at 0. So if Windows 7, is on the 4th line, it's entry 3.
Now change this line in /etc/default/grub to the entry number for Windows 7:
GRUB_DEFAULT=<the entry number for Win7>
The disadvantage of this, is that if you add other entries (even a simple kernel upgrade can cause this) before it, you must change it again.
A more fool-proof way is the set GRUB_DEFAULT to the title of the Windows 7, ie: if the entry is 'Microsoft Windows 7 (on /dev/sdb1)', set:
GRUB_DEFAULT="Microsoft Windows 7 (on /dev/sdb1)"
You may also want to set the default time that GRUB waits before booting the default entry:
GRUB_TIMEOUT=<no. of secs to wait>
Remember to update GRUB's boot configuration script after any changes to /etc/default/grub:
su -c "grub2-mkconfig -o /boot/grub2/grub.cfg"