Preparation

opkg update && opkg install cfdisk resize2f

Confirm drive device

df -h

Example output

# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root                 4.3M      4.3M         0 100% /rom
tmpfs                   996.3M     70.8M    925.6M   7% /tmp
/dev/loop0                1.0G     77.5M    926.6M   8% /overlay
overlayfs:/overlay        1.0G     77.5M    926.6M   8% /
/dev/sda1                15.7M      5.5M      9.9M  36% /boot
/dev/sda1                15.7M      5.5M      9.9M  36% /boot
tmpfs                   512.0K         0    512.0K   0% /dev

Resize

Run:

cfdisk /dev/sda

Choose the last one and resize

Quit and reboot.

After reboot, run:

resize2fs /dev/loop0