I realise I am always correcting and criticising my teenager. How do I change?

That awareness itself is a good start, because constant criticism wears down a teenager's spirit and pushes his heart away. The Prophet ﷺ taught: “Indeed, gentleness is not found in anything except that it adorns it” (Sahih Muslim, Kitab al-Birr wa as-Silah wa al-Adab). Try to balance every correction with sincere, specific praise, not empty praise. Before correcting, ask yourself whether the matter is truly important or just because you are tired. Pick one of his good qualities and mention it to him today. When correction really is needed, deliver it privately and briefly, not in front of others. See educating the family.