You may not be able to remove the Master HDD and still have a working system.
If you chose to Dual Boot you will be stuck with the original HDD because if you remove it the system will no longer boot.
If there is any possibility of you removing the original Drive at some point in time you should Clone your Current HDD to the New One and set it as the Master and the Old one as the Slave and then when you are certain you have recovered all of your Data & Settings format it and use it as a Storage Drive in this system. Or remove it completely fit it to a USB Caddy and use it for Backup after reformatting it.
If you want clone the original drive to all of the new space you can use either Acronis True Image Workstation Trial from here
http://www.acronis.com.au/enterprise/download/
Or PC Inspector Clone Max from here
http://www.pcinspector.de/Sites/clone_maxx/info.htm?language=1
Col
Col