un-syncing photos

I have my mac, i-phone, and -pad synced so that my photos from one device show up on the others. I would like to delete all photos from my phone and start again, so that I only have my camera roll (starting anew) and a folder of hand-selected photos from my computer on my phone (which I would also like to then show up automatically on my i-pad). I would also like to keep all of the photos from my i-phone just on my computer (i-photo) so that I have a copy of them all.