Hi,
From the manual, page 119 and 120
To perform a factory data reset.
1 Before you start, make sure to back up any important data that is saved on the
internal memory of your device to a memory card or other non-internal
memory.
2 From your Home screen, tap .
3 Find and tap Settings > Backup & reset > Factory data reset.
4 To delete information, such as pictures and music, from your internal storage,
mark the Erase internal storage checkbox.
5 Tap Erase everything.
6 If required, draw your screen unlock pattern, or enter your screen unlock
password or PIN to continue.
7 To confirm, tap Erase everything.
Your device does not revert to an earlier software version of Android™ when you perform a
factory data reset.
If you forget your screen unlock password, PIN or pattern, you can use the device repair
feature in Xperia™ Companion to erase the security layer. You need to provide your Google
account login details to perform this operation. By running the repair feature, you reinstall
software for your device and you may lose some personal data in the process.
To do a software repair, you can use Xperia Companion.
Further information an d the manual can be found on the support page of your device.
