How can I remap windows and alt keys in OS X?

• In System Preferences | Keyboard | Modifier Keys you can swap these two keys.
• Double Command is a PrefPane that offers many options for using Windows-keyboards (see the 3d & 4h checkboxes in the screenshot on that page). I'm not sure it offers advantages over the standard keyboard preferences, but perhaps it includes automatic sensning or a quicker way (hot key?) of changing back and forth.

Under the Keyboard System Preferences pane there is a button for "Modifier Keys" which allows you to remap command/option/control on a per-keyboard basis. There is no need to use an external tool to switch the keys.

I'm using OSX El Capitan and Microsoft Sculpt keyboard.