Format android to join internal memory partitions?

I have searched around the net but not really finding exact problems nor solution related to mine.

I have a tablet which should have 8gb of internal memory but the problem is that it have divided memory onto 2 partitions as data storage and internal storage and i have lack of space on my data storage as its only 1gb while other partition uses rest of the internal storage.

So i cant install any more apps as my data storage is full while second partition is almost empty.

I have actually tried to flash emmc and new android but i got the same partition sizes.

My device is BlueBerry Netcat M-28, this should be rebranded chinese Cube tablet as i know. Anyway the model is from 2014 and uses:

Android 4.2.2 Baseband version MOLY.WR8.W1315 Kernel version 3.4.5 build Jan 2014 HKT(i guess this is hong kong time)

Mediatek ARM Dual Core MT8312 1.2GHz

There is an option on tablet to move app to internal storage but that doesn't work well, many apps don't like to move. For example if i want to move facebook is still uses half a space of entire app on data storage, so i guess it only moves some irrelevant files to internal storage. And plus it stops working. it's the same with Skype and some other apps too. So basically i can move to second partition only files like music pictures videos.