Exchange some jazz with a German (5-2)
I believe the answer is:
trade-in
'exchange' is the definition.
(trading in is a kind of exchanging)
'jazz with a german' is the wordplay.
'jazz' becomes 'trad' (trad jazz is a type of jazz).
'with' means one lot of letters go next to another.
'a german' becomes 'ein' ('a' in German).
'trad'+'ein'='TRADE-IN'
'some' acts as a link.
(Other definitions for trade-in that I've seen before include "Article used in part-exchange" , "Trained (anag.)" , "Old item given in part payment for a new one" , "Older article used in part payment to retailer" , "Something used in part exchange" .)