Change, putting feet up (4)
I believe the answer is:
swap
'change' is the definition.
(swapping is a kind of changing)
'feet up' is the wordplay.
'feet' becomes 'paws' (paw is a kind of foot).
'up' is a reversal indicator (in down clue: letters go upwards).
'paws' reversed gives 'SWAP'.
'putting' acts as a link.
(Other definitions for swap that I've seen before include "Wasp (anag)" , "exchanged gift" , "Exchange, substitute" , "exchanged item" , "Substitute' feet backwards" .)