There is a completely painless way to import and delete photos on your iPhone or iPad, if you use a Mac. Now, I have not tested this on all Macs, but I suspect most Macs would be able to do it.
1. Connect your iPhone or iPad to the Mac.
2. Launch the Image Capture tool by typing “Image Capture” in the Spotlight search bar (the magnifying glass found in the top right corner of the entire screen).
3. Import and delete as many or as few photos from your iDevice as you’d like!
Command + A is select-all, allowing you to select all of the photos and movies shown.
Pressing Command + mouse left-clicking allows you to select multiple items.
Shift + mouse left-clicking allows you to choose all photos within a range.
That should do it.