Surprised that you haven't got an answer by now. I tend to look through my folders and get rid of any old documents, picture, etc that I will never need again but I'm a bit of a hoarder and never get rid of enough. Then I put them on an external drive and copy to the new system. Programs start from fresh. I back up my emails and transfer them across too.
What is ransomware and how do I protect my PC from WannaCry?