To do a good job with any new paint, all the old stuff has to come off. You can do this using a combination of chemical wood stripper, a power washer, and a thorough sanding (once all the old paint is gone).
Besides being a ton more work than installing new siding, you’ll also have to follow safe lead handling procedures every step of the way. This involves protecting yourself against inhaled lead dust, and then collecting all the lead paint chips you’ve removed, then dealing with them as toxic waste. All in all, not a great prospect for siding that’s probably already on its last legs.
I recommend cedar sidewall shingling as one option that’s both durable and attractive. You can apply wood shingles directly over the old siding, and then leave them unfinished. They last for decades.