Better qualified student engaged in refined exercise (7)
I believe the answer is:
upgrade
'better' is the definition.
(thesaurus)
'qualified student engaged in refined exercise' is the wordplay.
'qualified student' becomes 'grad' (graduate).
'engaged in' means one lot of letters goes inside another.
'refined' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'exercise' becomes 'pe' (Physical Education).
'u'+'pe'='upe'
'grad' put inside 'upe' is 'UPGRADE'.
(Other definitions for upgrade that I've seen before include "Improvement" , "'Improve, travel status perhaps (7)'" , "Raise to higher standard" , "advance" , "Raise in value or esteem" .)