This really depends on how you installed. Some partition types are easier to resize than others. The most important thing to do is backup everything important before you do anything.

Then boot to a live CD and you can use something like gparted or KDE Partition Manager to delete the NTFS partition and resize your Linux partition.

If you have a spare drive with enough space, it’s a great idea to take an image of the whole disk using Gnome Disks. That way if anything goes wrong, you can restore to the point you took the image.

Look up a tutorial on how to resize specifically your partition type (luks, ext4, btrfs, etc) with KDE PM or gparted. That should inform you of any caveats you should be aware of beforehand.