How to adjust valves

My '99 S10 2.2L 2WD has a slight tick coming from the engine. It seems to me to be the usual sounds associated with an out of adjustment valve. The question I have is, are my valves adjustable? I find nothing for adjusting them in the manual, or the Haynes guide. Are they supposed to be self adjusting and I am supposed to leave them alone? I'm not sure.

The valve lifters are hydraulic and no adjustment is possible.