The Ubuntu partition can simply be formated. However, if you do so, you won't be able to boot into windows anymore because GRUB will still sit on the first part of your disk but it will be broken. In order to repair this, you need to boot off a windows cd and do a repair by using the command "fixmbr".
Whether freespire is a good product depends on your expectations. Why do you remomve Ubuntu? If we knew, we should be able to make suggestions for another distro.