don't change a winning team; if it ain't broke, don't fix it

the more things change, the more they stay the same

climate change

(informal) to have a change of scenery, to get a change of air

(informal, figuratively) to change one's tune, to start singing a different tune

to change one's attitudes; to change one's tune

(figuratively) to change sides, to box the compass / (figuratively) to switch teams (to change one's sexual orientation)

to change horses in midstream

(simile) to flip-flop, to chop and change

(epistemology) paradigm shift (change in thinking from an accepted point of view to a new one, necessitated by scientific discoveries)