Use the link below to download Media creation Download Tool. Make sure you pick the correct bit version.
http://www.microsoft.com/en-ca/software-download/windows10
After you have downloaded the Tool, run it.
You have 2 options with the download....................
1. select
Upgrade this PC now, and then follow the instructions to finish the upgrade
2. select
Create installation media for another PC. This will start downloading the Win 10 ISO file to your computer.
You can then burn the ISO file to a bootable DVD or USB and use it to do the install, or
you can just simply go to the downloaded ISO file > right click at it > click Mount > click Setup.exe. This will start installing. You have the choice of keeping your files, settings and apps or keep nothing.
If during the installation you are asked to enter the product key, pick the SKIP option and continue.
Since you have had Win 10 before, activation after installing will be automatic.