I currently have no space left on my hard drive, but I want to increase my Ubuntu partition which would also require me to decrease the size of my Windows partition, but will doing this with Gpart or the standard windows partition manager cause any loss of data? If it will, is there a safe way of doing this?
Only use Windows partition manager to reduce the size of that partition. Windows 8 (and probably windows 7) will shrink its partition while the operating system runs, and ensure that there is minimal data loss. There is always a possibility that this will not work, so backup what you need to.
GParted can be used to increase the size of, or add a partition to, your Ubuntu system. You will probably need to boot from a live CD (or USB) to be able to perform this task, and it does take a goodly amount of time to complete. After booting from the USB, open a terminal and type
sudo apt-get install gparted
which will install gparted onto your USB. You can then run the program from the USB to dismount the HDD Ubuntu partition, resize it, and remount it.
You may want to double check, but I think you would want to use Windows to make its own partition smaller, and linux to use up that free space afterwards.