Change line of footwear (4-4)
I believe the answer is:
flip-flop
This clue could be a double definition.
'change line' is the first definition.
'flip flop' can be an answer for 'change' (thesaurus). I'm not sure about the 'line' bit.
'footwear' is the second definition.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for flip-flop that I've seen before include "Informal footwear" , "Shoe held on by a toe-thong" , "Light shoe" , "Rubber-soled sandal" , "Rubber sandal" .)