Not enough room on account, why? help!

Hello! I'm a prezi user and I keep getting a notification every time i try to upload photos:

Your file could not be added

There is no more space on your account.
You can add more space by upgrading your account.

I deleted some of my other prezis but I still can't add any pictures to the prezi i'm working on now. Even though I have enough space Prezi won't let me do or add anything, please help i need to finish this presentation tonight :(