VRV has every episode of Lupin the third for free with ads. Lupin part one all subbed, lupin part two dubbed for the first 79 episodes, subbed for all of them, lupin the third part 3 subbed, Lupin part 4 and 5 subbed. So far easiest way to watch them all but if your looking for dubs (Part 4, and 5) then would have to go through another route.
VRV is basically just Crunchyroll and Hidive put together in one thing so you can also watch all the Lupin I listed through Crunchyroll too if you want too