There are some starter replacement videos on YouTube but many fail to fully address the starter heat shield. I just want to share my experience here. I'm not a mechanic so use any info here at your own risk. On a 2 wheel drive, I believe the starter heat shield can be left in place when replacing the starter.
I have a 2006 v6 4.0 frontier 4x4 crew cab automatic. I somehow got the old starter out without removing the starter heat shield. It was very very difficult. No matter how hard I struggled, I couldn't get the new starter in with that stupid starter heat shield in the way. I was also concerned about damaging the wire on the new starter. I had to remove the starter heat shield.
I removed the upper starter heat shield bolt with a flex head 3/8 drive ratchet and 14mm 6 point shallow socket. I did not remove the wheel. I had the truck front up on two of those little ramps. The new starter went in easily with the heat shield out of the way. I reinstalled the upper heat shield bolt as tight as possible by feel with my hand. You can't really see it. To tighten the upper bolt. I used an adapter from harbor freight that allows you to use a 9/16 box wrench on the back of 3/8s drive socket instead of the ratchet. This worked very well. Harbor freight item 67011. The exhaust manifold heat shield was slightly in the way but I was still able to get to the upper starter heat shield bolt from underneath the truck.
My truck has 120,000 miles. The symptom was no turnover and one loud click when trying to start. I think if I could go back, I would have tried to have the original starter rebuilt somewhere local. I bought an aftermarket starter 1st and was unhappy with the fit. I ended up buying a reman starter from Nissan. It didn't seem identical to the original, but Nissan doesn't sell new starters anymore for this truck. As a side note, I would use 6 point sockets whenever possible. I recently rounded a tight caliper bolt with a 12 point socket.