As far as deleting any "locked" files go, clean method is described here: https://www.wikihow.com/Delete-a-Locked-File (both procexp and Safe mode options are viable and pretty clean). If you don't mind getting your hands dirty, I had good results with software Unlocker (http://www.emptyloop.com/unlocker/). Unlocker can actually do a lot of damage when used unproperly, but deleting temp files of whatever should be ok, simply make sure software whose temp files you are about to delete is not running and also make sure that they don't containg anything you could need (browsing history, etc.)
When it comes to freeing up space in general on Windows machines, I usually hardcore deleted all I could from
C:\<user>\AppData\Roaming. This icludes TEMP directories (you can delete all it allows you to, needed or in-use files are protected) and usually big space monger were leftover files from uninstalled software. So just go through mentioned directories by hand and if you see directory named after software that is no longer installed and you don't want to save its configuration, just delete it and empty Trash Bin after.
Also, delete Cache of your browser (it should allow you to do it from its Settings), online games and clear your Download folder (since it is usually full of unneeded things and is not cleaned by Windows Cleanup tool).
Lastly, delete all movies you already saw, they usually take majority of disk space :)
P.S.: Empty Trash Bin after all of theese as trashed items still can take disk space.