when to change spark plugs

hi freinds t
gr8 site for mazda owners.... guys i have a small problem i have this mazda 3 2005 model 1.6 engine problem is tht i feel tht the car initial pick up is very slow it used to be gr8 when i bought it and now i feel its gone down ,,,,, wt can be the reason .... is it a spark plug and plug wires tht i have to change will tht make a difference..... car has done 65000 km and its going goood jus worried for the pick up of the car .. plz advice