Here are some easy steps, you follow while clean Installing Windows 10.

Step 1: You need to download Windows 10 ISO from Microsoft.

Step 2: Create bootable USB of Windows 10 or Create a bootable DVD of Windows 10, and boot from the bootable media by making appropriate changes to the BIOS/UEFI.

Step 3: While installing Windows 10, you will read the following screen instructions, where you are asked to enter the Windows 10 product key. Since you don’t have a product key for Windows 10, follow the instructions in the next step.

Since you’re clean installing Windows 10 after complete upgrading from Windows 7 or Windows 8.1, you should skip the product key box blank, and click the Skip button instead to proceed further.

Step 5: Complete the installation of windows 10. That’s it! Your Windows 10 will activate online automatically once you connect your device to the internet network.

But if you are still having any activation issues, don’t hesitate to chat with Microsoft support or request a call back from Microsoft support.

Note: That above-mentioned steps is provided by Microsoft, and is not a workaround to illegally Activate windows 10.