Windows 10 has released almost one year, Microsoft Claims that owners of this new Windows are rapidly increasing, but not everyone will buy what he says, after a month trial, many users began to find ways on how to erase system partition of Windows 10, many of which still can't get use to the metro style, the flat style inherited from Windows 8, so here is the solution for your search, of course, if you are looking for how to erase Windows Vista before install Windows 10, you are already here.
Run Disk partition Wiper, if you don't have it, download one to try; click on the boot partition, always Drive C as the system partition, then "Wipe Now" bottom to go on, at the meantime, a warning message pop-up to make sure if you confirm, "Yes" to type "Wipe", the wiper does the rest, then there's no Windows 10 in your disk any longer.
Suggestion: if you want to reinstall new system with portable USB or any facilities alike in a clean disk, "Wipe Disk" is a good choice in Disk Partition Expert tool, when you meet the same alert, click "Yes" to confirm wiping whole disk within system and data partition.
The other way is to use the default setting, back to previous system, in control panel, if the previous one is data clean and runs really faster than the new one.
Users of Windows Vista are not that much now, especially when Windows 7 and Windows 10 released, some of the users may erase Windows Vista and directly install Windows 10, the newest. Fortunately, Disk Partition Wiper supports Vista System; you can run it or download Disk Partition Expert to Wipe Disk if the data in those partitions are less important.
The question put out by Shaon actually doesn't complicate, if you have Windows Vista in partition D, Windows 7 in Drive C, you can just use Disk Partition Wiper to "Wipe Volume" on the Vista Partition, then dooing a "Format Volume" operation to redistribute the space. What Shaon had done was common when Windows 7 first released, many people still have multiple boot systems in different volumes, if you would be a fan of a certain Windows System, and other volumes within systems might be wiped like this.
See also: how to wipe hard disk partition