The programme's plot - in which a distant relative stands to inherit the estate - will be downplayed and the series running time cut from eight to six hours when it airs in the US next week.
Downton Abbey focuses on the inner workings of the English aristocracy, specifically a legal device called the 'entail', which determines how an estate should be divided up.
In the show, written by Julian Fellowes, Lord Grantham (Hugh Bonneville) learns that his heir has died on the Titanic and the next-in-line is Matthew Crawley (Dan Stevens), a middle-class third cousin he has never met.
However, US broadcaster PBS feels that the nuances of the British aristocratic system will be lost on American viewers.
"We thought there might be too many references to the entail and they have been cut. It is not a concept people in the US are very familiar with," said Rebecca Eaton, executive producer for PBS.
"American audiences are used to a different speed when it comes to television drama and you need to get into a story very quickly. We also wanted to get to the point where Matthew Crawley arrives on the scene much faster than in the British version.
"He is a pivotal character and his arrival brings with it drama and conflict. In the British version he doesn't arrive until episode two. In our version he is there in episode one."
Despite the cuts to the broadcast version of Downton Abbey, the entire series will be released in the US on DVD, billed as the 'British Original'.
Downton Abbey was a surprise hit for ITV last year, drawing almost 11 million viewers for its final episode. The broadcaster has already commissioned a second series.