How to delete system files while i'm rooted?

Hello everyone, i have a rooted phone GT-I8262 and i used to delete the system apps before by ES Explorer or root explorer, though i'm now facing a problem with a file that i can't delete, it says you have no permission to do it, this app is called (DU battery saver) each time i uninstall it from my phone and restart the phone, it shows me that black screen after the boot logo which is (android is upgrading) so after i open the phone, i see that (Du battery saver) is installed once again.. i had to go to the system files apps folder and couldn't find it there, so i found it in another directory in DATA/APP folder, so i tried to remove it by 2 kind of file explorers like ES and root explorer and after giving them the permission of root. but i couldn't remove it, is there any way to remove such protected apk files?

please help, thanks