Log into your Account, and click on the "Language" tab

Click the dropdown menu to select the Course that you'd like to customize

OR, you can choose "Global Strings" to customize the text for ALL courses

Once you've selected your course, you'll see a table that looks like this:

You can use the search function here to find any piece of text:

Once you've selected your text, you can change the translation here:

Your course will now show the new translation for this text