You have tow options with the factory reset or hard reset of the Sony Xperia M4 Aqua Dual. Much like the other phones in the Xperia range, the M4 Aqua Dual reset can be done by entering the rest code into the mobile phone or it can be done via the menu on the phone.
As you will know, the mobile phone once reset to the default factory settings means that all your data will be wiped off the mobile phone. Think of it as formatting your computer and resetting it back to the way you had received it when you bought it brand new. This is no different. It will wipe out your APN internet settings, phone book and all other data on the phone. Most people do this when they are going to sell the mobile phone and wish to remove all personal data and settings.
If you are changing mobile phone and wish to backup all the data first, then you will need to use the Xperia PC Companion which is available on this website.
Note that once you have reset your mobile phone back to factory settings. You can then connect your phone to the Xperia PC Companion and then move the backed up data back onto your now factory reset mobile phone. You can also move this data onto a new mobile phone if it is in the Xperia range.
Note that once reset you cannot recover the data which has been deleted. Note lastly that these codes are for the E2333, E2363, E2312 mobile phones.
Hard Reset will erase all of your data
All described operations you are doing at your own risk.
Hard Reset Sony Xperia M4 Aqua Dual using Menu
Hard Reset Sony Xperia M4 Aqua Dual by Code