Pick up again (5)
(Other definitions for renew that I've seen before include "Revive" , "what regeneration will do" , "Give fresh life to" , "Reinforce" , "Invigorate" .)
'pick up again' is the definition.
('learn' can be a synonym for 'pick up' so perhaps 'relearn' is OK for 'pick up again')
This is all the clue.
(Other definitions for relearn that I've seen before include "Mug up once more" , "Acquire knowledge again, having forgotten it" , "Study what one has forgotten" , "Become aware of again" , "Recommit to memory" .)