Firstly, you will need to log into your account and click onto Product Manager > Media > Upload images. As shown in the red boxes in the screenshot below:
On this next page you will have to option to either drag and drop you image files into the grey section. Alternatively, you can click on Add files and then select them from your computer as shown below:
Once you have opened your files, the popup box will close and you will start to see your images begin the upload process. Once it has completed you will see the below:
You will now be able to find that image in your Media Directory.