Do i need to save windows 10 software in order to have it without buying it again ect.? what should I do
David: Various methods here. You won't need to buy a new copy of Windows 10.
1) If the drive is still working you can make a recovery drive – go to control panel, recovery and follow the prompts – you will need a blank USB drive
2) if the drive is already dead on a working computer you can make a Windows 10 USB installer from Windows 10 media creator
3) you could clone the old hard drive to the new if the old drive isn't too far gone with free cloning software such as Macrium reflect – in this case you would end up with an identical clone and all your programs and settings intact. If the failing drive has many errors the clone will probably detect this and abort.
No, you can download the Win10 installation from Microsoft's web page, and make a bootable USB drive with that.
Then fit your new blank hard disk, boot off the USB drive and install Windows. Skip the part where you enter a licence key. Because your hardware has already been activated, when the new install checks it activation status the MS servers will already have your particular hardware on record, and the new install will simply activate automatically.
If the hard drive is still functional buy a new one and clone the old one onto a new one.
In a Desktop, there may be another slot
In a laptop or where there are no open slots you can buy a USB-SATA converter or enclosure
Cloning software is free on the internet
You can replace the hard drive, and reinstall Win 10 before buying a new license. If you replace the machine, then you need a new license.