How to perform an `UPDATE` on a whole varchar column by removing the last word?

Every row has a value like `one two three lastword` `one two lastword` `one lastword` (there is no row with value just `lastword`). Fortunately, all words are separated by 1 space. I want the `lastword` removed (and its preceding space character) for the whole table

`lastword` is not a unique word, i used this just for example. every row has its own last word, (so i cannot just replace `'lastword'` with `''`)