How to delete an iCloud backup?

My iCloud is almost full, it can no longer backup my iPhone because there is not enough memory in the cloud. I want to delete the current backup in the cloud but every time I go to Settings>iCloud>>Storage & Backup>Manage Storage>Marc's iPhone, it only shows when the last backup was, 4/30/13, and the backup size, 3.9, and "Delete Backup", but when I click delete backup a window comes up that says "Cannot delete backup this backup cannot be deleted because it is in use" but like. I want to delete it and back up my new stuff without using my Macbook. Anyone know how to make the backup delete?

Toy may try via your computer: