Before beginning any work, make sure to disconnect the negative battery cable from the battery. I've replaced a starter in my Nissan, it was a 5 speed not a auto.If it is a manual you have to remove your cluch pedal link that's connected to the transmission .From there you have two bolts to remove for the starter from the transmission.I believe it is a 14mm socket one side you'll need a extension. Make sure to unplug all the wires to the starter.I believe the auto is the samething.If this helps or you need more info just write to my e-mail. I still have my 1992 Nissan.
Simple thing to do-And I am no automechanic by any means. Remove battery cables to avoid shocking yourself....buy ramps from Craigslist....ramp and remove anything in the way....which if you buy the 6 inch extension for your ratchet (which you will need to buy to get past something on the top bolt) you almost don't even have to move anything.....except the oil filter which I think if you wanted you might be able to jiggle it out even around that...since it is only about 3 pounds (compared to 15-20 pounds in a truck starter)...but the two bolts that hold a starter in are simple to remove once you find them.....It takes an hour just to ramp and find the starter. The easy way to find it is to follow the negative battery cable which is black with a yellow stripe or two.....and the bottom one is easy to reach but hard to find while laying under the car..... I suggest removing the starter and taking it to the store for testing first...and if it tests bad....then you don't have to shell out 32 dollars for the core charge....and you know the actual problem is the starter. So the oil will drip on you and you will be working under a car which can be a little scary....but the bolts came out easy on mine....and when you put it back in make sure you tighten them or you will be back under there the next day tightening them like I was.
As a side note: this problem hit us in one morning....no warning...so I thought it might be a bad problem since usually starters go slowly...but ours just died...probably just the selonoid which could have probably been repaired...but for 90 dollars I would rather just replace the whole thing.
Additional info: The starter is tucked up under the intake manifold. It is held on by two 14mm bolts. One is accessed best from under the car. The answer above suggests removing the oil filter. That is messy. I recommend removing the "A" shaped intake manifold brace. It is held in by three 12mm bolts. With that out of the way, access to the bolt is much easier. The other bolt is easily reached from on top of the engine. It is the same bolt that the battery ground is attached to. You also have to remove the main power cable from the end of the solenoid and there is a clip on electrical connection on the starter bracket. I found that a swivel adapter and a long extension made getting at the lower bolt much easier. One hour to get it out and less than an hour to get it back in.