delete pictures from cloud

If you mean photo stream photos, they don't count against your iCloud storage so deleting them won't free up space in your account. If you want to delete them to free up space on your phone, open your my photo stream album in the thumbnail view, tap Edit, tap the photos you want to delete, then tap Delete. Note: this will delete them from iCloud and all devices connected to your photo stream.

If you mean camera roll photos, import them to your computer and delete them as explained here: http://support.apple.com/kb/HT4083.

The only data you can manage from your computer is the data on icloud.com (Mail, Contacts, Calendars, Notes, Reminders and iWork documents). Of these, Mail is probbly the only thing with much size. You could try deleting old emails that have large attachments that you no longer need, but that may not free up enough space.

Otherwise you may need to try to cancel the backup by disconnecting your router from the internet and letting it time out. If the iPad is still frozen and unresponsive after doing this, or if the backup fails to stop, you may need to try resetting you iPad by holding the power and home buttons at the same time until you see the Apple logo, then release.

Question, when I delete on one device it still appears on others? Why does this happen?