You can download the IDE from this Help Center article (or in the Welcome to Learn section of Learn.co). Make sure you read through the article and that your system meets the requirements before you get started.
If you have an older version of the IDE (anything before 2.4.0), make sure to uninstall the old version before downloading the latest version. If you do have the latest version (2.4.0 or later), you can follow these same steps to update the IDE without uninstalling.
Step-by-step guide on Windows:
Step-by-step guide on OSX: