Not a teacher nor a native speaker.
If you want to speak like an American or British you need to live there at least 5 years (or even more) I think.
You can't speak without an accent even if you enrol in English courses in your locality. You can find enormous quantity video about AmE and BrE on Youtube. There are huge number of articles about it as well. Moreover, if you want to improve your speaking you must speak as much as possible. (preferably to native speakers). You can improve your pronunciation by listening to something (I listen to the BBC Radio 4 extra).
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