To migrate any files you may want to keep, you will need to mount the partitions and the copy the data over from one partition to the other.
The easiest way to Uninstall ANY operating system is with OS-Uninstaller
The Ubuntu Wiki about it is here
to install it, boot to Ubuntu and then do the following in the terminal...
sudo add-apt-repository ppa:yannubuntu/os-uninstaller
sudo apt-get update; sudo apt-get install -y os-uninstaller && os-uninstaller
This will install and run OS Uninstaller, just select the OS you want to remove...
then click Apply in the confirmation window.
The selected OS will be removed and your GRub(bootloader) files will be updated to remove the OS from the boot Menu
I would suggest that you remove OS Unistaller after you have used it to avoid any unfortunate removal mistakes in the future, You will likely not need it again soon and it is easy enough to reinstall if you need it again....