to stop taking sth you’re addicted to completely, without any medication.
go cold turkey
to replace something old with something new
out with the old, in with the new
a new beginning
a fresh start
to start from zero
to start from scratch
to start from the beginning without any advantage or previous work done
turn over a new leaf
to stop doing something you repeatedly do, like a bad habit
kick the habit
to work hard and successfully at a new activity straight away
hit the ground running