Hotpoint FF71 Mistral Freezer thermistor removal

Good Morning. Following problems with my fridge freezer, fridge section not cooling, but freezer working OK I first ensured that behind the air vent and all areas on the bottom were fluff free, and that the compressor was working, I then turned it off allowing it to completely defrost for 48 hrs. After that it worked perfectly for a day or so, but then the problem repeated itself. I should mention that I had read all the advice within the forum prior to investigating what could be the cause. To cut a long story short, I ordered new thermistors for the freezer section. However I seem to have a problem actually disconnecting the two plugs on the old thermistors, the green and the yellow ones…Do these connectors have a locking system at the socket? I’ve tried with no success to disconnect them, and don’t want to cause any damage by using excessive force. Thanks in anticipation!