Changing from triangle to new shape (8)
I believe the answer is:
altering
'changing' is the definition.
('alter' can be a synonym of 'change')
'triangle to new shape' is the wordplay.
'triangle' can be anagrammed to 'ALTERING'.
But, I am not sure how this is indicated.
'from' acts as a link.
Can you help me to learn more?
(Other definitions for altering that I've seen before include "Modifying, changing" , "Changing -- 1 across (anag)" , "making a change" , "Making changes" , "revising" .)