Hi @Radbeh, let me see if I can help out here.
The latest version available for the Z5-series is Android 7.1. If you have an older version of Android, you can update the phone either using the settings of the phone (Settigs > About phone > Software update) or using Xperia Companion and a computer.
I hope that answered your question. If there is anything else on your mind regarding your phone, let me know! 
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