От добра добра не ищут

There is no need to make drastic changes in the existing state of things or way of life because you can never be sure that the changes will be for the better. See Ладно уселся, так и сиди (Л), Лучшее - часто враг хорошего (Л), Не от хлеба ходят, а к хлебу (H)

Cf: Don't budge if you are at ease where you are (Br.). Don't quarrel with your bread and butter (Br.). If you have a good seat, keep it (Br.). If you have bread, don't look for cake (Am.). Leave (Let) well alone (Br.). Leave (Let) well enough alone (Am., Br.). Never quit certainty for hope (Am., Br.)