如何设置默认操作系统

我的系统是Win7和Ubuntu双系统，Ubuntu用wubi安装的，我现在默认进入的操作系统是Win7，
怎么修改让默认进入的操作系统是Ubuntu，因为我不想在每次开机的时候去选择
Ubuntu这个菜单后进入Ubuntu
这是我的gurub.cfg文件内容[code]#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by /usr/sbin/grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
load_env
fi
set default="0"
if [ ${prev_saved_entry} ]; then
set saved_entry=${prev_saved_entry}
save_env saved_entry
set prev_saved_entry=
save_env prev_saved_entry
set boot_once=true
fi

function savedefault {
if [ -z ${boot_once} ]; then
saved_entry=${chosen}
save_env saved_entry
fi
}

function recordfail {
set recordfail=1
if [ -n ${have_grubenv} ]; then if [ -z ${boot_once} ]; then save_env recordfail; fi; fi
}
if [ ${recordfail} = 1 ]; then
set timeout=-1
else
set timeout=5
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/10_lupin ###
menuentry "Ubuntu, Linux 2.6.32-23-generic" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-23-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro quiet splash
initrd /boot/initrd.img-2.6.32-23-generic
}
menuentry "Ubuntu, Linux 2.6.32-23-generic (recovery mode)" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-23-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro single
initrd /boot/initrd.img-2.6.32-23-generic
}
menuentry "Ubuntu, Linux 2.6.32-22-generic" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-22-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro quiet splash
initrd /boot/initrd.img-2.6.32-22-generic
}
menuentry "Ubuntu, Linux 2.6.32-22-generic (recovery mode)" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-22-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro single
initrd /boot/initrd.img-2.6.32-22-generic
}
menuentry "Ubuntu, Linux 2.6.32-21-generic" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-21-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro quiet splash
initrd /boot/initrd.img-2.6.32-21-generic
}
menuentry "Ubuntu, Linux 2.6.32-21-generic (recovery mode)" {
insmod ntfs
set root='(hd0,7)'
search --no-floppy --fs-uuid --set 071944d50f40a610
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /boot/vmlinuz-2.6.32-21-generic root=/dev/sda7 loop=/ubuntu/disks/root.disk ro single
initrd /boot/initrd.img-2.6.32-21-generic
}
### END /etc/grub.d/10_lupin ###

### BEGIN /etc/grub.d/20_memtest86+ ###
### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry "Windows 7 (loader) (on /dev/sda1)" {
insmod ntfs
set root='(hd0,1)'
search --no-floppy --fs-uuid --set cc18007a18006634
chainloader +1
}
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###[/code]