Acer Aspire One upgrade to Windows 10?

[Windows Central Question]

I upgraded my Acer Aspire One to Win 10 with no problems, except it is running very, very slow. It hasn't broken any speed limits over the last year however. It used to be fairly brisk. Something is wrong, but it was wrong when I was running Windows 7 starter. I thought maybe the OS was damaged in some way, but maybe too many processes are just clogging it up. It's has 70 Gb of HD space available and it's not reporting any errors, so now I think I maybe need another 1Gb of RAM and a clean install. Is there a possibility that I can recover the previous OS, which is 7, and then do a clean install or can I do a clean install while 10 is the OS? I like the Acer because it's lightweight and so easy to drag around with me.

Thanks for any advice.

Renne