When you turn it off, all memory is lost. You usually end up with pseudo-random patters. To actively clear all mem would require a machine language program ... which would be wiped in the process.
Windows handles the virtual memory and there really isn't a way to clear it. Virtual memory is stored on the hard drive. It basically uses your hard drive as more RAM. You can't clear virtual memory...
You can Format all drives. While formatting drives, when you format C Drive all the ntldr files and important OS files will get deleted. Or you can reboot the computer.
Go to the files you want to delete and click delete that will send them to the recycling bin. Delete them from there and they're out of the way. The good side about this is that if you suddenly need...