I'm not an expert on the situation, but I do know several of the changes.

The primary one is the vanguard of the proletariat concept. Rather than the workers leading themselves, Lenin envisaged a hard working, motivated group of intelligentsia leading the people. They'd do all the thinking per se, so we got the benefits of communism.

I also think Lenin changed the idea of the withering away of the state (the socialist stage would involve a dictatorship to level everyone out, at which point, an overarching government becomes irrelevant and dies off). The idea being his vanguard would live on.

Another major change is the origins of the revolution. Lenin basically dragged Russia into communism, instead of the people rising up. Besides popular support on St Petersburg and Moscow, the Bolshevik movement wasn't really the people. The Menshevik idea is more Marxist- wait for the revolution, try and help the workers along the way.

And then Lenin advocated skipping straight to socialism, ignoring capitalism (Russia was mostly feudal and not considered really ripe for a socialist uprising at that time). This is where the dictatorship of the proletariat comes in, another change. The political system would be dominated by the proletriat, capitalists would be excluded, but a form of democracy in the soviets (working councils). In practice, democracy went out the window with the Civil War, and didnt really return until Gorbachev.

The entire changed doctrine became known as Leninism (http://en.m.wikipedia.org/wiki/Leninism), and varied widely. Lenin ended up supporting small scale capitalism in the NEP to revive the economy after all. After the NEP my knowledge is limited even moreso however. And there's probably more changes I've missed.