The links below have instructions for deleting photos.
iOS and iPod: Syncing photos using iTunes
iPad Tip: How to Delete Photos from Your iPad in the Photos App
Another Way to Quickly Delete Photos from Your iPad (Mac Only)
How to Delete Photos from iPad
How to: Batch Delete Photos on the iPad
(With iOS 5.1, use 2 fingers)
How to Delete Photos from iCloud’s Photo Stream
Photos on your iPad that were taken with the iPad or copied from emails, websites, etc. are downloaded to your computer using the image capture application on your computer. The exact application depends on what computer you have. Once those photos have been transferred to your computer they can be deleted on your iPad.
Photos that were copied to your iPad using iTunes on your computer during a sync process are removed by doing another sync. After you connect your ipad to your computer and select it in iTunes on your computer go to the Photod tab and deselect all the albums you want to remove from your iPad. Then click on Apply or Sync. The photo albums will be deleted from your iPad but they will remain, if they were still there, on your computer.