Updating these older devices is often restricted because official support ended years ago. However, you can still perform a factory reset or attempt to install custom software. Restoring or Resetting Your Device
Go to Settings > Privacy > Factory data reset . This will erase all data and return the phone to its original out-of-the-box state.
If you are looking to "obnovit" (restore/reset) the device to its original factory state to fix performance issues:
* Boot to recovery: with device powered off and the cable disconnected, hold Volume down & Power keys until the device vibrates. *
Unofficial builds for Sony Xperia devices - Page 4 - iodé community
To get a newer version of Android, you would need to "flash" a custom ROM.
This process requires unlocking the bootloader and can "brick" (permanently disable) your device if done incorrectly. Key Maintenance Tips
(now part of Sony Xperia Companion ) on a Windows PC. Connect your phone via USB to check if any final official updates are available for your specific model.

