2003 Nissan Altima 3.5 SE - Rough Idle

My 2003 Nissan Altima 3.5 SE is idling rough. The car has 64,000 miles on it and I've had issues with the car in the past. When I 1st purchases it (1 year ago, w/ 48,000 miles) the car drove fine for about 6 months, then it was bucking and such. I brought it to the dealer and in the end they had replaced the Mass Air Flow sensor twice, the car's computer twice, the cam sensor, fuel pump, & engine mounts.

Well, now I have a rough idle, I'm assuming I need a tune up, but I bought the spark plugs to replace myself, but it appears the rear 3 plugs are under the throttle body. I just want to know if this is somethng I can do or if I should bring it to a mechanic?

Thanks.