How you said "I've lost two stone"? (7)
I believe the answer is:
lightly
'how' is the definition.
Both the definition and answer are adverbs. Perhaps there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for lightly that I've seen before include "Readily" , "With gentleness" , "easily" , "in delicate fashion" , "without good reason?" .)