Verified answer

Sometimes the U.S version is changed slightly, such as adding an extra sentence in places. And I think the title of "Harry Potter and the Half Blood Prince" is "Harry Potter and the Half-Blood Prince" in the US version, but it could just be later versions.

The U.K. version has less pages b/c the print is smaller.

Mostly the vocabulary, taking out words that only Brits would know and putting in American ones.