By finding out what you're worrying about specifically and realizing that every possible worry is a fear that a particular promise of God's Word is a lie, won't work in this situation, can't be trusted, isn't for me, etc., etc., etc. And then just study the Word of God that covers that area and devote all of your focus to that. Worry is one of the bigger sins, along with strife. Most people think adultery and murder, but where there's strife there's confusion and EVERY evil work according to the book of James, and worry's nothing but inner strife that ultimately bottomlines in unbelief in a particular promise or group of promises of God's Word because of spending more time with the problems than with the particular promises that cover that situation.
Worry makes a metallic vice out of your mind and you will CRUSH whatever you worry about because you're just tightening the grip over and over and over again as though you were in a wood shop turning the handle on a vice. Thinking positively WON'T build anything positive in your life, but it'll give you a greater emotional basis for speaking the Word of God and having His Spoken Word come to pass in your life. But worry will cost you everything you've got and everything you ever hoped to have and it will strangle all of your dreams, all of your energy, and remove absolutely each and every single possibility from your life. It's not just a part of the human equation. Worry is to your spirit, soul, and body the equivalent of trying to live on nothing but pork rinds and lard. You know that something would totally give where your body is concerned if you tried to do that, right? Plus it would be totally disgusting to try to live on nothing but that, right? It's totally toxic.
Tolerate it as much as you'd tolerate a snake bite. Your emergency room for your worry is God's Word and Isaiah 54 is a great place to start. You could read through all of 1John aloud half a dozen times a day every single day for the next 12 months and be totally transformed by it. People that have never taken God's Word as medicine before though will probably balk at the idea. But I already know where they're headed anyway, so I'm not worried about that. I know what works in my life 100% of the time everytime that I put it to work. And anytime it's not working in my life, then I back up and realize that I'm talking about doing it more than actually doing it. And that never works.
I won't get into details, but there are certain particular Scriptures that I still read aloud each and every single day, many times throughout the day, and I've already been the total embodiment of the substance and evidence of those particular Scriptures for years. But as your body will never outgrow it's need for a steady diet of chlorophyll, and even if you were at your ideal body weight and muscle mass that would only mean that you'd need it all of the more to maintain what you've got, it's the exact same thing with the Word of God to your spirit and emotions. No such thing as anything that any of us can say "I already know that." All of life is progress or regress. There's no such thing as staying still in one particular chapter of yourself that you've achieved. Even God is still growing in everything that you can think about Him.