WNDR3700v4 resize partitions

Hello guys,
I recently installed OpenWrt 18.06.4 on my router, and root partition has 12M available while /temp has over 60M

Filesystem                Size      Used Available Use% Mounted on
/dev/root                 2.5M      2.5M         0 100% /rom
tmpfs                    61.0M    752.0K     60.3M   1% /tmp
/dev/ubi0_1              14.0M    876.0K     12.4M   6% /overlay
overlayfs:/overlay       14.0M    876.0K     12.4M   6% /
tmpfs                   512.0K         0    512.0K   0% /dev

Since I'm new to openwrt can someone help me to understand how can I add more space to root.

Thanks in advance

You will notice that /tmp is tmpfs filesystem which resides in RAM. You can't use that for permanent storage. Data is lost after every reboot.

You will notice that / and /overlay are similar and are the overlayfs which reside in flash. You can read about overlayfs in the wiki

You can run dmesg to see the partition layout. Don't think you can do much as a user to change size

If your looking to increase storage size read this

https://openwrt.org/docs/guide-user/additional-software/extroot_configuration

You can use GParted. Here is a very simple guide: http://derekmolloy.ie/resize-a-virtualbox-disk/#prettyPhoto