$ sudo fdisk -l
 
# list shows:

Disk /dev/mapper/omenius--vg-omenius0: 40 GiB, 42949672960 bytes, 83886080 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x640262c9

Device                           Boot    Start      End  Sectors Size Id Type
/dev/mapper/omenius--vg-omenius0-part1          2048 33554431 33552384  16G 83 Linux
/dev/mapper/omenius--vg-omenius0-part2      33556478 41940991  8384514   4G  5 Extende
/dev/mapper/omenius--vg-omenius0-part5      33556480 41940991  8384512   4G 82 Linux s


# But when I do:
$ sudo fdisk /dev/mapper/omenius--vg-omenius0

# and then: d (delete partition), n (new partition), enter (default start), enter (default end)
# but still when I press p for listing the info, I get exactly same rows as above, so still 16G :(