Constamtly downloading Android OS ......

Hi all,
I installed on my old MicromaxE313 Mokee 5.1.1
Now I realized that Android OS is comstantly downloading something and in 3 days it used 4GB of my data. I am not sure but it is possible that is is only on WIFI, not on SIM data. What is going on? How can I switch off tis downloading??