June,
Vickie is correct in her post. The message you received is due to your having uploaded more images than your plan allows. For the $2.95 plan, your allowance is 500 megabytes and for the $9.95 plan and the $19.95 plan the limit is twice as much, or 1 Gigabyte.
As things stand you will be billed for the overage. However, if you delete some images right away to get your image hosting storage back underneath the plan limit, you can file a support case and ask them to credit you for the extra amount you will be billed. You can find out how much storage you are using currently; here is an FAQ that will tell you how you can easily do that.
As far as how to delete images, there are several methods you can use. We've got a tutorial that explains these; you will find it by clicking this link.
I hope this is helpful to you.