When I installed my 128 GB Samsung 840 Pro, I first shrunk the C: partition on my HDD down to about 109 GB. Then I used the Samsung "Data Migration" software to clone my C: drive to the new SSD. The process went very smoothly, after I updated the software.
I haven't done much in the way of changes to my old HDD. I still have Windows 7 installed there and if I ever have a problem with my SSD I can just switch the boot order in the BIOS and be up and running on my "old" Windows installation in a jiffy.
Yogi