The first and most obvious task is to delete files you no longer use. Granted, this chore will likely take a while since you may bump into hundreds or thousands of files you no longer need. To do this, open File Explorer, jump to the folders that contain your documents and other personal files, sort your files by modified date with the oldest ones appearing first, and then simply scrap the old and unneeded ones.
Another method to put the kibosh on unneeded files in Windows 10. Click on the Start button and then select Settings > System > Storage. Click on your main hard drive at the top of the window. Windows 10 calculates the types of files on your drive and how much space they take up. Click on a particular file type such as Documents, Pictures, or Music.
Empty your Recycle Bin. By default, any file you delete remains on your hard drive via the Recycle Bin so you can recover it if necessary. But at some point, the bin will get big, so you'll want to prune it. You can double-click on the Recycle Bin to view and delete any individual files you no longer need, or you can right-click on the Recycle Bin icon and click on the Empty Recycle Bin command to purge all the files within.
The Windows Disk Cleanup tool can get rid of a whole mess of files in one shot. Click on the Start button and scroll down the Apps list, open the Windows Administrative Tools folder, and then select Disk Cleanup. The Disk Cleanup tool displays a series of file categories and determines how much space you can free up per category. Click on each category to view a description. In some cases, you can also view the files in that category. Click on the checkmarks next to the categories you feel comfortable deleting and then click the OK button.
Source & more info: PC Magazine
