Heyy You!
Firstly if your phone has Recovery then it is easy....
Just Reboot into Recovery by recovery combo...
in most cases it is Volume Up +Home + Power ON...
Ok....?
But What About those devices who don't have Preinstalled Recover E.g Micromax A35
>Download Android_USB_Driver For your Device...
>Download Android Multi Tools (Google it)
>Install Drivers....
>Boot Your phone into Fast boot Mode by Volume Up+Power On...
>Open Android multi tools as admin...
>Type "8"=Wipe Cache and Factory Reset...
>Your Device Will Get Restarted Automatically...
Note:- By Doing So You Will Loose all Your Data Stored in internal memory.....