I posted this on another thread, I hope it is of some help
Firstly, I am assuming you have a copy of these images stored safely elsewhere ?
What I am going to describe is not the most elegant way of deleting your images, it is a variation of deleting one at a time but much swifter.
Open the photo app on the iPad, select the left hand photo button which should then display all the thumbnails of the images you have on your iPad, click the top right hand button with the arrow, on the left three buttons appear, one of which is delete. If you put your finger on the first image you want to delete the blue & white arrow is seen, without taking your finger from the screen run your finger over the other thumbnails and in succession the tick will be seen against the images, the delete button will show the number of images you have selected, when you are satisfied click the delete button.
As I said not elegant !
17" MBP ( late 2009 ) Mac OS X (10.6.4) Photography, motoring, European travel