Step 1: Go to Media Tab
Click on Media under Side-menu
Then click on the Upload Button.
Step 2: Upload Box
In the Upload box, click on Browse which will directly open you to your local storage, select an image/video from it or you can also drag a file and put it in the space provided.
Click on Upload.
A private option is available if you want to upload media publicly or not.
Your image or video will be successfully added to your Media collection.
Video Guide on How To Upload Media