Replace the lifters

Get a manual from an auto parts store. It will give you a step by step instruction on how to do the job. It will also have the bolt torque values needed when you reassemble the engine. If you're going that far into the engine, do a camshaft and timing chain too. Replacing one lifter will affect timing on that one cylinder which will cause a rough idle that you can't fix.

M10 bolts: 1st step; - 18 ft./lbs. 2nd step; - turn 60 degrees 3rd step; - turn 60 degrees M12 bolts: 1st step; - 22 ft./lbs. 2nd step; - turn 60 degrees 3rd step; - turn 60 degrees
2.0 Engine

Your lifters ride on your camshaft. You must remove your intake manifold to get access to your lifters. And you can not just replace the lifters! Your engine is a flat tappet cam and lifter setup, you must replace all 16 lifters along with the cam and a proper break in procedure must be followed, and I highly suggest a ZDDP break in additive be used. And there will still be a good chance of the cam wearing out upon break in thanks to our legislators removing the natural zink and phosphorus lubricants from engine oil.

Step by step is too much typing here. Auto parts stores have manuals specific to your car. It will also have the torque values for all the bolts necessary to complete the job.

Here is a step by step guide; Not your year so check the tech manual for specs but the procedure is the same

DIY Adjusting the Valve Lash clearance on 03 Maxima Nissan Forum

Because the lifter leaks down when the engine is cold and then pumps up later tells me that the lifter is faulty and needs to be replaced. I would recommend using someone who is qualified for the job. This isn't a skill level D job.

I tried the DIY service and repair manuals from a website and it actually helped me repair transmission problem in my jcb 3cx site-master. it wont move
forward or reverse, engine is good both solenoids for forward and reverse work.
I don't have much technical knowledge but I just followed it step-wise, and works perfect! got it from www.reliable-store.com

I had the same problem , Come to find out it was the crank barring's and not the lifter's. Take one of the crank barring's off and feel the crank where the barring goes and if it's rough it's more in likely the crank and not the lifter's but if it's smooth put the crank barring back pull the valve cover's and there's the lifter's , pull the nut off the lifter's and pull the lifter rod's out roll them on a flate surface to see if there bent. Then go to a auto part's store and get the haynes manual it will tell you everything you need to know.

Remove valve covers, remove rocker arms and push rods, remove intake manifold, remove lifters, (special lifter tool may be required). Reverse steps to reassemble. Make sure to use new gaskets. 

depends, how long between oil changes, how many miles, try and engine flush, sometimes debrise adn sludge will cause a lifter to stick and not move freely causing the tapping noise you hear, if this doesn't fix or quiet the problem it may be to far gone, but if you really love the car get a tear down manual and go to work....put aside a weekend and about 500 dollars it'll be a job