Well shaving your legs won't make it worst if you do it in proper way.
You can use electric razors as it might be soft and less irritating.You can also use traditional blade razor but rmember to moisturize your skin before you shave.Make sure you won't get cut while shaving as cuts and trauma can lead to new patches of psoriasis, which is known as Koebner's phenomenon.
Other options might be Waxing as it lasts longer than shaving but waxing sometimes lead to serious skin irritation and allergy.