How can I delete files off my Mac?
Choose the file and press Cmd+Delete. then empty the Trash.
Cmd (command) is beside the space bar.
You can use CCleaner. They now have a file cleaner for Mac, cleans files from Firefox and Safari.
If you want to delete files and application as well as cleaning your OS, I recommend you to use CleanMyMac. It's a good application with good reputation among Mac users.