The simplest explanation is to find British songs, TV shows, movies, podcasts and listen to them. Find an accent you like and work on that. Immerse yourself, and repeat what you hear. To native speakers, there are very clear differences between US and UK English (without even thinking about Sth Africa, Australia, NZ, Canada, and so on): spelling, pronunciation, rhythm, slang, even the way you tell a story or joke can be different. Listen and try to notice the differences - we native speakers definitely notice them! :-)

There is only the difference of accent. Try to use less slang words as the Britishers do.

American or britain is countries that using english as a mother language .. And has no different