Can I replace a 19V1,58A charger with 19V3,42A laptop charger safely?

If "A" represents amps, I'd say you're good to go, the computer will not burn up if you plug it, and it should not be severely underpowered as well. Check for a few days and see if you face system stability issues. One downside will be longer battery charging times. If the amp rating of the power supply is reduced, the laptop will take longer to recharge it's batteries when they go too low.
 


I think he actually wants to do it the otherway around. Use a more powerfull charger. That will definetly not be good for you battery if the laptop will even charge at all. Probably it protect it's self from a too high Electric current.
 
Laurensschu is correct. If you're planning to replace a 42A charger and use a 58A charger as the replacement, that's not a good idea.
You could burn up the motherboard, or kill your batteries. The battery and the motherboard cost much more than the power cord, so if I were you, i won't take that chance.
 


I don't think the current is that high for his mini laptop. It's probably 1,58 Amps, so about 32W. And the other one is 3.42 Amps, which would give +/- 65 W. That's never going to be compatible.