You can hard reset or factory reset the Sony Xperia Z4 from the instructions below. There are two option like most Xperia mobile phones. The first is visa the menu and the other is via the Xperia PC Companion software which you can also find on this website. Remember that once you do a factory reset everything, all your data on the mobile phone is permanently gone.
You can search this website for other software as well. Note that if you want to backup your mobile phone before you reset it then the second option works best as you can backup your data on your phone onto your home computer and then reset the phone by using the same software.
The first one is if you do not wish to backup any data and simple want to reset the mobile phone.
Hard Reset will erase all of your data
All described operations you are doing at your own risk.
Hard Reset Sony Xperia Z4 Option 1:
Hard Reset Sony Xperia Z4 Option 2:
From there you simply click on update
It will update your software if older but if the software it already up to date then the next option is to click repair.
Now the next screen the resetting of the mobile phone will begin.
You mobile phone will now be hard rest.