Lexical change comes from various places.
From 18th century onwards, lexical change came from many avenues:
Technology - inventions are single biggest source of lexical change, whilst most have Latinate/Greek roots - some are created in different ways.
Travel - as travel has become easier - so to have our ways of picking up words. In Victorian times, Indian words came into our lexis from the Empire e.g. pyjamas, verandah, etc.
We now have more words from Eastern cultures e.g. Tsunami, kamikaze, karaoke.
In 20th Century lexical change has come from influence of the US as a superpower - many Americanisms has come into our language.