Disk Quota

I am getting the following message and I am not sure how to correct it can you help please! My customers are calling to say that they are getting an error when they try submitting a form. I need to get this fixes ASAP

Your account is currently over disk quota. Form submissions can not be added to your Form Manager for the form located at:https://clotheshelpingkids.org/Request-for-Pickup.htmlAll future form submissions for this form will be sent to this email address until you are under disk quota. Delete any unwanted or unused files or purchase additional disk space by logging in to your account.