Answer

There is a limit to how much you can shrink your C: partition in your Operating System as there are immovable Window system files stored there.

One tip: Try running a defragmentation of your system before attempting to shrink the size of  your partititions.  You can use the Windows Defragmentation Program to do so. A contributor to this article suggests the use of  Puran Defrag as it can defrag your Pagefile.

Another tip contributed by our community: You may also wish to temporarily switch off your Pagefile as you want your data to be stored and continually so in the front of your partitions. A recommended resource is  GParted--Live CD, which our contributor says is 'quite good for the resizing part'. 

Note that if you use a disk image to move your data to the new HDD drive you intend to install and you have a recovery partition, make sure you do read up on how to maintain it (the recovery partition) while resizing your other partition(s) for the new disk when moving the data over.