Do i need to change my 2002 kawasaki ninja 250 spark plugs?

I am new to motorcycles. Yesterday for the first time, the bike did not want to start. After ten minutes it finally started. is it the spark plugs? Are they easy to change? I forget i took the bike out two nights ago it was kinda chilly and it stalled at a light. i had a hard time getting it to start. any ideas? Thanks