The valve clearance is adjusted by measuring and replacing all 16 individual spacers called "buckets". I would only attempt this if hot clearance is out and wear is obvious. A rebuilt head might be a better choice.

I assume this is a used engine.
Some noise is normal. If the valves are sticking the noise will be worse. A good oil additive may help.

"Those who cannot remember the past are condemned to repeat it" -George Santayana