As early as possible, too many people try to make the change too late.
Keep on top of controlling diabetes now and before any complications and live a near enough normal life. Badly controlled diabetes is forever eating away inside of you, good or better controlled diabetes keeps the wolf away from your door for a while until you take your eye off the ball.
Unfortunately the damage is done when most realise they 'need to' change habits.
Good luck and try hard to stay in control