The update rolled out in parts of Russia, and will soon (in one, maybe two weeks) cover the whole territory of the country. It consists of both 7.0 Nougat features and August security patches. New features include new emoji, enhanced notifications, improved power saving, stability & optimalization improvements and more. You can just wait for the update to download on your phone automatically or, if you are impatient, head to Settings > About Device > Download Updates Manually and, uhm, download it manually. As always, make sure that your phone is charged and connected to wifi, as the update process will be relatively long and power consuming.