I've a system partition of 740GB which is way more than needed, I just need less than 64GB but I don't know how to unmount the system's partition since Ubuntu always needs it.
Number Start End Size File system Name Flags
1 1049kB 256GB 256GB ntfs Basic data partition msftdata
2 256GB 256GB 256MB fat32 boot, esp
3 256GB 260GB 4096MB linux-swap(v1)
4 260GB 1000GB 740GB ext4
I just want to shrink the system's partition (the ext4 one) to add another data partition, because, Ubuntu won't need a lot of space, 64GB is enougth for me.