At the top of the 'IEG Scripts' page is a 'Import IEG Script' link which lets you upload, or import, a new IEG script. When you click on this link, you will be presented with this screen which asks you to choose the file on your file system which contains the script definition and to provide a logical name for the script (the id, version number and type will be read from the script definition itself).
If the script you are uploading is intended to replace an existing script with the same id, then you should select the 'Overwrite' check-box, otherwise an error will be thrown.