How to move the root partition

You’ll need to boot from a live cd. Add partitions for them to disk 1, copy all the contents over (with rsync, see rsync clone partition), and then use sudo blkid to get the UUID of each partition. On disk 1’s new /, edit the /etc/fstab to use the new UUIDs you just looked up.

Updating GRUB depends on whether it’s GRUB1 or GRUB2. If GRUB1, you need to edit /boot/grub/device.map

If GRUB2, I think you need to mount your partitions as they would be in a real situation. For example:

sudo mkdir /media/root
sudo mount /dev/sda1 /media/root

(Filling in whatever the actual partitions are that you copied things to, of course)

Then bind mount /proc and /dev in the /media/root:

sudo mount -B /proc /media/root/proc
sudo mount -B /dev /media/root/dev
sudo mount -B /sys /media/root/sys

Now chroot into the drive so you can force GRUB to update itself according to the new layout:

sudo chroot /media/root
sudo update-grub

Then boot into the new grub entry, and when the system has boot, the

update-grub 

will update and set the first entry for the actual /dev/sda1 system