As you have installed Ubuntu inside Windows 7, select Ubuntu from the Windows boot manager and then you will see the Ubuntu GNU Grub2 menu.
(or after you select "Ubuntu" from the Windows boot manager, keep
Shift pressed and the Grub menu should appear)
Then press 'e' to start editing the boot entry.
And now you need to change a line in the GRUB2 boot entry from "ro" to "rw".
You will see a line similar to this:
linux /boot/vmlinuz-3.13.0-24-generic root=UUID=AAC884AC1F144321 loop=/ubuntu/disks/root.disk ro quiet splash $vt_handoff
Replace 'ro' with 'rw' and finally the code will look like:
linux /boot/vmlinuz-3.13.0-24-generic root=UUID=AAC884AC1F144321 loop=/ubuntu/disks/root.disk rw quiet splash $vt_handoff
F10 and you are done!
This is only to boot Ubuntu for a single time. You have to repeat these steps every-time you reboot. But you can change the 'grub.cfg' permanently to avoid this issue. Follow these steps to edit the 'grub.cfg' file after logging in to Ubuntu.
Open terminal (
sudo gedit /boot/grub/grub.cfg
and press enter.
Gedit will open with the 'grub.cfg' file.
CTRL+F to open 'find' box on gedit.
Type 'ro ' in the find box. (Remember to type a space after 'ro' - should be 'ro ', not 'ro')
Search results will be highlighted and then change all those 'ro's to 'rw's. (replace 'ro' with 'rw')
Save the file and reboot.