Windows 10 is currently in testing at the moment the latest build is (Windows 10 Insider Preview Build 10162) currently no significant bugs are found at the moment, however there has been an announcement from Microsoft that the build 10176 is likely to be a completed operating system if it releases to manufacturers this week.
Those who are ready to update on the 29th of July will have to go through Windows Update on either 8 or 7. If nothing works on that day or does not show in the updates here's why:
1. You do not have the latest service pack installed.
2. You are running a non-genuine copy of Windows and or pirated and torrented versions of the Operating System.
3. If you are on XP or Vista well you're out of luck.