Bolshevism does not exist as a theory. Bolsheviks was name of the party, not a theory. Leninism also does not exist per see, what exist is Marxism-Leninism, which is theoretical extension/modification of Marxism made by Lenin and his colleagues born from a necessity to actually implement Marxist theory in practice. Or in other words to reconcile Marxist theory with practice in actual conditions of Russia and Europe as experienced by Lenin and his Bolsheviks.

And yes, it is confusing.