A razor knife to cut through the old caulking. Just stick in the groove and cut til' you get through. I'll be tough to get the panel up , be patient. It will come up with persuasion but you will damage it with brute force. As for re-caulking it use GE SILICON II in almond or white ,depending on how faded your deck is from original.
HOT TIP, Use the blue painters tape to tape off around the groove the panel when you re-caulk it. Just put anywhere you don't want caulk. Allow the caulk to completely cure (usually overnight) then pull up the tape.
Been there done that........