To inflate or make something swell (transitively); also to exaggerate or enlarge a story or idea.
子どもたちは風船を膨らますのを手伝った。
The children helped to inflate the balloons.
彼は話を膨らますのが上手で、聞いていて面白い。
He's good at embellishing stories, which makes them entertaining to listen to.
宣伝で売上を膨らますために数字を操作した。
They manipulated figures in advertising to inflate sales.