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#21
No one said you had to buy anything. To download the 64bit flavor of 10 however you may find it a bit when going to run the MC tool while booted into 10 since the downloads are intended as upgrades and will detect already being installed. But even on 7 when going back I would have to make a few separate attempts so I have a complete set.
For you on the other hand only going for one flavor of one edition the choice will be whether or not to save the 64bit download as an ISO image file to be saved in a folder you can use multiple times in case you have to make up the media more then once or simply choose the dvd burn or usb option and allow the tool to see that done.
Remember you can replace the 32bit installation following the steps for a clean install without reformatting or repartitioning the drive. To have everything literally fresh however some will clean the drive off entirely to see a brand new primary OS partition go on for a fresh clean install of the OS which happens to be the swapover to the 64bit now that you have 10 activated from an upgrade.
In reference to the previous statement about when going to buy that was in regards to how the licensing works where you can choose to nuke the 32bit flavor in favor of seeing the 64bit go on or vice versa! MS isn't concerned about how many times you reinstall the same version, same edition of Windows over and over again as long as the hardware remains the same. Swap brands of memory some time and you will end up needing to call MS! Been there before.