Jupiter is not even a brown dwarf which starts at about 13 times the mass of Jupiter.

For upgrading Jupiter to a star, it would need 80 times its current mass.

There is nowhere else in the solar system enough mass to grow Jupiter but the Sun. Taking that mass from the Sun is in theory feasible but of course out of the range of our capabilities for quite some time.

That's for natural nuclear fission though which would waste a lot of energy going into space and not where we would want to have it (the moons).

It's probably more realistic to build small fission suns that orbit the moons that produce heat and light in a less wasteful, more directed manner. Still not possible today :-)

I thought this was interesting so did a quick search: it does not look feasible [0].

Note: even if it were possible, the small relative increase in radiation received by Earth may have a butterfly effect similar to greenhouse gases and make global warming even more difficult to manage than it already is.

[0] https://physics.stackexchange.com/questions/776/can-jupiter-...

You'd need a lot of monoliths.

Oh well, there are ways. Let me introduce the Stellification Engine:

https://www.orionsarm.com/eg-article/4a48d58c84350

A mass of self-replicating hot hydrogen dirigibles powered by fusion. They use part of the energy to stay afloat in the correct altitude and to repair and reproduce & radiate the rest outwards.

By igniting I assume you mean nuclear fusion. Jupiter does not have enough mass. So what would it take? Transfering mass from the sun to Jupiter I guess.

Not sure how much heating it would provide to its moons. It already provides an unhealthy amount of radiation.

Throw in more mass, than it will ignite itself and be the second sun.

Actually, when you think about it, Jupiter is a good candidate for a dyson sphere.

Just need a whole bunch of monoliths to up its mass...

Combustion requires wholesale access to oxygen.