Mend your ways
Definition 1 of 1
Pro Tip 1/3Behavior Focused
The phrase is about changing negative behaviors to positive ones. 
He realized that to make friends, he needed to mend his ways.
Pro Tip 2/3Urgency
Often used to suggest that change should happen soon to avoid consequences. 
After the warning, the employee knew it was high time to mend his ways.
Pro Tip 3/3Emotional Weight
Can imply disappointment or disapproval, requesting someone to improve. 
Her mother said sternly, 'You must mend your ways or face the repercussions.'