To install GParted, enter the command:
$ sudo apt-get install gparted
This video show how:
After resized and boot up Ubuntu MATE on Raspberry Pi 2, now I have 15.7G on a 16G microSD.
This page (eLinux: RPi Resize Flash Partitions http://elinux.org/RPi_Resize_Flash_Partitions) describes activities relating to partitions on the Raspberry Pi for Linux based operating systems, such as Raspian Linux. It may also apply to other operating systems too, but you should check. Incorrectly using the instructions is likely to corrupt your system.