Many people face problem on limited space provided by mobile manufacturers. I will show you how yo clear your android internal memory space.
There is a option in your phone go to system settings- storage- and there you will find phone storage and bellow that you will find erase phone storage you can click on erase all data.
But be careful before erasing all data you must check your data on phone storage. Check all your photos. What's app videos, images and database will be deleted. For mobiles like A77 what's app data is stored in phone's storage.
Copy all your photos and what's app videos to your external memory.
Another way is risky but you can do it yourself. I mean that you can swap your phone SD card with external SD card. Here I will show you how to swap.
First you have to root your phone. To root, you can use frama root click here to download frama root application for android which will root your phone automatically. It will ask you permission to grant so you then grant and then install ES explorer and and then grant super permission then go to device folder in ES explorer and then go to etc folder and find file called vold.fstab Then click on it then click on text then click on es note editor then on right side there is menu and click on it and select edit then change Sd card 1 an sd card 0 and save. Then restart your phone and it is done you will see your phone sdcard and sdcard has interchanged.