Simple, yes, to change surrounding area (4)
I believe the answer is:
easy
'simple' is the definition.
(associated in meaning)
'yes to change surrounding area' is the wordplay.
'to change' is an anagram indicator.
'surrounding' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'yes' is an anagram of 'esy'.
'esy' going around 'a' is 'EASY'.
(Other definitions for easy that I've seen before include "Like a walk in the park?" , "for a piece of cake" , "Far from hard" , "Gentle - light" , "Tranquil" .)