How to remove files that are on iCloud
You can use a feature called optimise storage to store old and unused files on iCloud.


Click the Apple Logo in the top-left
Select About This Mac
Click on Storage in the System Information window
Click details 


Then turn on Store in iCloud.



This uploads unused files to iCloud and deletes them from your Mac.

Alternatively, if you have a specific file you want to store on iCloud, go to iCloud.com and upload the file/check if it is there then delete it off your Mac.