Only one step is needed: Install Linux.

Yeah, sponsored by Avast. (Which is OK). A free PC cleanup utility is the CCleaner from Piriform: https://www.ccleaner.com Been a few odd reports about it of late but nothing to get exited about, just install it, check the checked boxes, i.e. you might not want your bin emptied or browser cache wiped, and run it once for Windows and once for applications. Normally you can delete everything without thinking twice. Don't download it from Filehippo and if it asks if you want some random extra bit of "free" software during the install process, the answer is no. Alternatively you can look under Windows Adminstrative tools in the menu and click on Disk Cleanup, select C and open. You can see what's taking up all the space on you drive and select and remove. Defragging doesn't do much if you have an SSD.