You're good-to-go...
 
BTW, I like the Tux!   

I have Windows 7, and I get bugged about the upgrade all the time, and put it off. My C: drive is a 128GB SSD, and I want to upgrade the SSD to a larger one and do a clean install of Windows 10 on that. How do I do this when I still have Win 7?

Download the Win10 Media Creator.
Use the Media Creator to download an ISO image file and burn that to DVD-R... or create a bootable Flash Drive installer.
 
Make note of your Win7 install key.
Install Win10... and authorize with your Win7 install key
 

I upgraded my desktop from Win7 just following the Win10 install prompts. Crossed my fingers and it worked, even though—at the time—I was still running an EMU 0404 card that used XP/Vista drivers. Perhaps it was my lack of concern that made things go so well.

I'm downloading the update now.
 
I had gone to Win10 before and had issues but realised they were down to my own borked install configuration.
 
I've backup up the Win8.1 install to 2 external drives so I can always roll back.

fireberd
Win 7 is eligible for the upgrade and even a clean install of Win 10, using your Win 7 Product Code. 
See this from the Win 10 forum:
http://www.tenforums.com/tutorials/23354-clean-install-windows-10-directly-without-having-upgrade-first.html 

I just checked this link. It is an outdated kludge for doing a clean install using the identifying data from a previous installation of win 7 0r 8. The versions of the media installation tool that are available from MS now, do not require that you use a previously activated installation of Win7 or Win8. You can install to a new machine so long as you have the product key from a qualifying version (even if never previously installed) of Win 7 or Win 8. There are a bunch of unofficial instructions on this, http://www.howtogeek.com/224342/how-to-clean-install-windows-10/
but MS has now posted their official instructions:
https://www.microsoft.com/en-us/software-download/windows10?34de222e-6944-44aa-8f45-8e96988880a4=True 
expand using the media creation tool
expand perform a clean installation using a USB or DVD
 
The difference is that you will need to enter the product key for the qualifying version during the installation. This is much easier than the kludge in fireberd's link which seems to require that you copy an xml file from a previously activated installation.