My Windows 10 was really slow, I was really frustrated so I decided to dual boot Ubuntu. I only put 100 Gigs on it because I wasn't sure if it was a great idea (I have 400gb in total). But it was a love at first test, so I wanna get rid (uninstall) of Windows 10 and put all the 400gb on Ubuntu. The question is, how do i go about doing that? thanks in advance.
You can accomplish this process with virtually any live bootable media that includes
gparted up to and including your Ubuntu 16.10 Live media that you likely used to install your system. If you still have that handy there is no need to create another bootable media. You can eliminate your Windows partitions from within your Ubuntu installation, but to resize your existing Ubuntu partitions you should boot from live media.
You can achieve this by creating a GParted live USB (http://gparted.org/livecd.php), and then use it to remove your windows partition, and grow your Ubuntu Partition
EDIT: You will probably have windows reserved partitions too, such as the recovery partition. You can remove those as well, as long as you have/can make a windows recovery disk later, if you decide to go back.