What is the Space Upgrade?
Free WordPress.com blogs come with 3000 megabytes (~3 GBs) of space for storing uploaded files and images.
The Space Upgrade gives you an additional 5, 15, 25, 50, or 100 gigabytes of storage space, and allows you to upload music in addition to images. You cannot upload audio files or music without the space upgrade.
To upload and embed videos directly onto your blog, you need to purchase VideoPress. The new policy is active since May 6, 2009. All video blogs with active space upgrade before or on May 6, 2009 automatically received a 1-year free VideoPress subscription.