Amateur with aim to improve (5)
I believe the answer is:
amend
'improve' is the definition.
(I know that improve can be written as amend)
'amateur with aim' is the wordplay.
'amateur' becomes 'am' (as in am-dram).
'with' says to put letters next to each other.
'aim' becomes 'end' (both can mean a goal or purpose).
'am'+'end'='AMEND'
'to' is the link.
(Other definitions for amend that I've seen before include "Revise" , "make an improvement" , "Modify, correct" , "Put right" , "Ameliorate" .)