From SKYbrary Wiki
Only users belonging to the group Authors or Contentmanagers group can manage files. They can upload images and other files and they can replace existing versions with new versions.
Upload a file
- In the sidebar, under toolbox, click "Upload file"
- Next to the Source filename, click Browse to locate the file on your computer.
- Change the Destination filename to something descriptive, if necessary.
- Fill in the Summary, if necessary.
- Click the Upload file button.
After you've uploaded the files, they can be used in articles.