by pepedog » Tue Feb 12, 2013 10:11 am
There is no easy way to do this, and I don't know what media you have now.
The pi must boot from an sd card, 1st partition is fat32 hand has kernel and firmware. It gets mounted as /boot later.
I would get what packages are installed now (pacman -Qq), less kernel
Boot from sd card, mount old media, make a directory on it called old, move everything on it into that folder
Copy whats on second partition on card to root of old media
Edit cmdline.txt to point to old drive as rootfs
Now you start pi again with root fs on old media, update and install packages, pick an choose what data and config you want from the /old directory.
Warning, always sync before reboot, and to turn off use poweroff command
If you have a new drive for the pi that's a different story, with both running you could rsync data over the network