When you're editing content, click the 'insert' menu:
Then click the word 'Upload' and select your file.
Alternatively type or paste in the URL to a location where the image resides, and then specify the dimensions you want for the content
Wait for the image file to upload, and then click on 'OK'
The URL will accept most video providers, such as YouTube, Vimeo, Brightcove, etc. And can handle large video file uploads.