The usual challenge facing a new prime minister usurping a predecessor mid-term is how to make the “change” they promise without entirely trashing the work of the previous administration, ie, their own party.
If they more or less stick to the same policies but with a different “style”, then people might wonder what the point was in replacing the old leader. If they opt for a more radical approach, then they risk breaking solemn manifesto commitments, alienating old regime loyalists and confusing the general public.