I now have a 1 TB ext4 partition, but I can't change that with gparted.
How can I partition the hard disk into 600GB and 300GB?
Should it stay as ext4 or should I change it to NTFS?
I have only one OS installed.
I now have a 1 TB ext4 partition, but I can't change that with gparted.
How can I partition the hard disk into 600GB and 300GB?
Should it stay as ext4 or should I change it to NTFS?
I have only one OS installed.
Based on subsequent comment, you wish to preserve your Ubuntu 17.10 install and create a new 18.04 install in the other partition. You can repartition that drive without losing the original installation.
It requires rebooting with a LiveUSB, and then running gparted to shrink the current partition, leaving space at its end to create a new partition. Save the changes, shut down, remove the Live USB, and power back up; you will then have two partitions. The first partition, sda1, will be bootable and contain your operating system and the apps installed with Linux as well as any added after installation.
In the future you may wish to consider keeping your data in a separate partition, by assigning /home to that partition. Then, since all your data goes into /home with normal use, you can be assured that any new install will not alter your data.