How to enlarge rootfs_data and enjoy the full storage on my router?

Hi there.
Bought a new Cudy X6 V2, which has 32Mb of storage (apart from 256Mb of RAM).
Used this FW:
as well as the one they offer on their website:

Both create an effective storage of 5.8Mb.

The problem: After updating all the updateable packages, you run out of space before even start working.

How do you change the rootfs_data size to enjoy the 32Mb this device has to give?

Here is what I grabbed from the The OpenWrt Flash Layout


There is no extra space available, so to be simple : you can't. Don't buy a device with so few flash memory. 64MB is the strict minimum, more is welcome.
But you can try the extroot method if there is an USB port (I can't find a picture for the exact device).


this, you should never do -