Step up to change side associated with undesirable elements (9)
I believe the answer is:
inclement
'step up to change' is the definition.
I can't judge whether this defines the answer.
'side associated with undesirable elements' is the wordplay.
'side' means to remove the middle letters (I've seen 'sides of' mean this (only the letters on the sides remain)).
'associated' becomes 'meant' (meaning is a kind of associating).
'with' says to put letters next to each other.
'undesirable elements' becomes 'incle' (I can't explain this - if you can you should give a lot more credence to this answer).
'meant' with its centre taken out is 'ment'.
'ment' after 'incle' is 'INCLEMENT'.
Can you help me to learn more?
(Other definitions for inclement that I've seen before include "(Of weather) cold or wet" , "lacking mercy" , "with heavens opening?" , "Unpleasantly showery" , "Stormy" .)