Reply to Headshells and needles

I am new to turntables and can't find a good article on the upkeep and upgrading of needles and headshells. I have 2 Stanton str8-80's that have what look like normal headshells and Stanton needles.

I would like to upgrade these as the one on the right definately doesn't pickup as good a signal as the one on the left. Do I need to replace both or just the needles? Thanks for filling me in.