Renounce Frenchman, say, on the way up (6)
I believe the answer is:
renege
'renounce' is the definition.
(I've seen this before)
'frenchman say on the way up' is the wordplay.
'frenchman' becomes 'rene'.
'say' becomes 'eg'.
'on the way up' says the letters should be written in reverse.
'eg' reversed gives 'ge'.
'rene'+'ge'='RENEGE'
(Other definitions for renege that I've seen before include "Deny or renounce" , "Fail to honour an obligation" , "Fail to keep promise, or revoke in cards" , "Go back on an obligation" , "South American cowboy" .)