Didn’t find any info on how to achieve this from google so knocked up a quick video:

Forgive the amateur-ness! It’s amazing how a 60second task takes 5minutes when trying to stay “on camera”.

The steps I note on the video:

1) Pop the front cover off by levering from the “hitachi logo”
2) Undo the 2 screws now exposed
3) Pop the top off
4) Remove the 6 screws now exposed
5) Remove the disk/rails etc
6) Remove the 6 screws from the rails
7) Slide the disk out

Currently the cheapest source of a 3TB drive seems to be from inside this Hitachi XL3000 available today @ scan.co.uk for £107.98 inc VAT http://www.scan.co.uk/products/3tb-hitachi-xl3000-0s03093-35-external-desktop-hard-drive-usb-20-black