Where do I put the purchase key in the trial version

I bought aseprite a long time ago, and now I’m trying to get it on my new computer (the new computer is windows and older one is mac so I cant copy the files) I’ve found out that somewhere in aseprite you can input a key (which I found) but I can’t find where to input the key. Can someone please help cause I don’t want to use my crappy old mac to make pixel art. Also I didn’t buy it on steam, I bought it from the website.