Can a bicycle with 26x1.95 tires on magnesium alloy wheels be upgraded? Say 26x2.10?
Most of the time that should work. You have to make sure it isn’t a Schwinn special sizing (Any of the S(1-6) sizing). Make sure the tire ISO and wheel are 559mm.
For this bike, I would say with 99% confidence that would work.
Personally, I would look elsewhere if you were looking to upgrade something. A used bike from a reputable brand on Craigslist will perform a lot better for the same cost.