Here is very simple bash command to format partition, mkfs.
Format will erase all of your data. Please be careful to run.
My example, I format partition with ext4 file system.
-t : describe specific FILESYSTEM
-V : show detail
$ sudo mkfs -V -t ext4 /dev/sdc1
Now my partition has changed from NTFS to ext4.
Check partition with fdisk again.
$ sudo fdisk -l