tc@box:~$ sudo fdisk -u /dev/mmcblk0

The number of cylinders for this disk is set to 322688.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/mmcblk0: 3965 MB, 3965190144 bytes
3 heads, 8 sectors/track, 322688 cylinders, total 7744512 sectors
Units = sectors of 1 * 512 = 512 bytes

        Device Boot      Start         End      Blocks  Id System
/dev/mmcblk0p1            8192       69631       30720   c Win95 FAT32 (LBA)
/dev/mmcblk0p2           69648       93119       11736  83 Linux

Command (m for help): d
Partition number (1-4): 2

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2
First sector (8-7744511, default 8): 69648
Last sector or +size or +sizeM or +sizeK (69648-7744511, default 7744511): +40M

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table
fdisk: WARNING: rereading partition table failed, kernel still uses old table: Device or resource busy

tc@box:~$ sudo reboot

tc@box:~$ sudo resize2fs /dev/mmcblk0p2
resize2fs 1.43.1 (08-Jun-2016)
Filesystem at /dev/mmcblk0p2 is mounted on /mnt/mmcblk0p2; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
The filesystem on /dev/mmcblk0p2 is now 29296 (1k) blocks long.