how to update the menuentry

grep menuentry /boot/grub2/grub.cfg
This will display all your grub entries

Highlight the entry you want to default to - for example Windows 7 (loader) (on /dev/sda1) Right click and choose copy

Type

gedit /etc/default/grub
Change the entry

GRUB_DEFAULT=0
to

GRUB_DEFAULT="Windows 7 (loader) (on /dev/sda1)"
i.e. paste the entry you want (including the quotes)

Save, then type

grub2-mkconfig -o /boot/grub2/grub.cfg