How do I change the GRUB boot configuration from within Windows?

The hard part is editing your Linux filesystem from Windows. FS Driver supports writing ext2, but I don't know of any good tools for ext3 or 4 (and these SU and SF questions aren't encouraging), let alone any other filesystems you may have used on your boot partition

But if you do manage to get write support for your boot partition from Windows, actually changing the saved default is easy. First you need to do some prep work in /boot/grub.conf. Change default to saved, and add savedefault 0 (where 0 is Fedora's index in the GRUB configuration) to the Windows block so booting into Windows will reset the saved default back to Fedora

Then from Windows you can edit /boot/grub/default. Delete the line that's there (it'll be default or 0 most likely), and change it to 1 or whatever the index of your Windows install is. When you restart, GRUB will read that file (since your default is saved) and boot into Windows, and the savedefault line will change that file back to 0 for future boots

If you have a /boot partition formatted as FAT32, you'll be able to edit grub's config file from both OS(es).

You can use Grub2Win or other similar programs as listed here. They offer an easy user interface.

You could also completly remove Grub and boot both systems from the Windows bootloader. In order to do so you need to use tools such as EasyBCD.