I have an Ad-Free account that says that I have 500MB of disk space and as per instruction in the 'Free Accounts Upgraded' thread, I have created this support ticket.
Please check what CPanel lists as your disk space. CPanel controls how much of the disk you can use, the account panel may not be up to date. If you continue to have an issue, please post back and I will as a staff member to assist you further.
Now that your initial question has been answered, I am going to close this thread to mark it as resolved. Feel free to create a new support request if you need more help or have any additional questions.