Want to try Linux. How hard is it to go back to Windows if it doesn't work for me?

I think I'll like Linux based on what I've read. I think I've settled on Mint Cinnamon (although I was considering Puppy since the computer I'll be putting it on only has a 32GB Flash HDD). The computer in question came with Windows pre-installed. It's a Dell. I don't know where my product key is or how to find it, but some online say you don't need it. What's the real story there?

I use this computer for schoolwork only, which includes learning to code in Python and maybe R. Any advice?

But mostly the only thing stopping me from trying Linux is the worry that I won't be able to go back in the event that I need to.