Welcome.
In brief:
1. GParted is able to modify ntfs partitions in the hard drive (resize, move), so it can do what you want. I guess that C: is the system partition, that was small and now it is almost out of space. It is quite usual.
2. To expand a partition, you need to have some unallocated space immediately after or before that partition. This means that if your unallocated 45 GB are located elsewhere in the drive, you have to manipulate other partitions, i.e. move/resize one or more other partitions to place the unallocated at the needed place.
3. Be careful in the case of logical partitions: if the unallocated in in an extended partition, you have to resize the extended partition too, to make the unallocated adjacent to the partition to grow. Furthermore, in the case of more than one logical partitions, don't change the order of them in the extended partition. Logical partitions out of numerical order are source of problems, because many tools don't understand the partition structure. GParted screen shows the partition numbers in graphical format.
4. It is highly recommended to take backup of the data before doing any modification. In most of the cases there is no problem. In a few cases however some problem might occur, that can be the desaster for the system. Even a hardware problem (drive, bad connectors, power failure) can be fatal. I remind that there is no "undo" for applied operations, and it is not at all recommended to break a running operation; it could damage the filesystem. Professionals take even double backup before proceeding.
5. It is recommended to go step by step. Although it is possible to schedule a lot of operations, I think it is safer to make one operation each time, reboot into windows at least 2 times and allow the check of the partition by the operating system. This is longer, but I think safer because ou can verify that the system behaves as expected.
6. GParted doesn't work for the dynamic microsoft drives.
7. You can work with the GParted livecd. It is a bootable cd that works entirely on the RAM. The current stable version is 0.4.6-1. Please, don't use any of the newer testing versions. To resize the C: partition (usually the first on the drive), you have to change the end point of it to the right in the graph. Please, leave the "Round to cylinders" box unchecked for this operation, because otherwise an unwanted move of the entire partition could occur.
8. Try to defrag the partitions 1-2 times and run the chkdsk command before proceeding. Complicated partition structures can lead to errors.
(Moved to the live media section)
*** It is highly recommended to backup any important files before doing resize/move operations. ***