The easiest way would be to click on the iRite instance and click on the edit button in the properties inspector. HTML Editor will convert the instance to an HTML editor instance automatically. Make sure you delete your WA_iRite folder afterward, since you will no longer need this folder.
Another way you could do this is to just delete the iRite instance and WA_iRite folder and add an HTML Editor instance in.
Also, make sure you uninstall iRite before installing the HTML Editor.