How can I get another car key (Car, Nissan Primera Activ, 2001?

I bought a Nissan Primera Activ car (Hatchback) and now the car-key is sometime difficult for me to open or lock the car. I mean the point on the key where I have to press so as to either open or lock the car is very stiff, and now difficult for me to do. How do I get another key?