t's important to manage your time. You can't just stay in front of the computer all day.
Start by taking 10 minutes of what you usually play. Keep doing that and getting used to playing less.
WTF or whatever site you go on is fun, but you don't HAVE to go on for more than 2 hours.
So manage your time.

And play outside, read a book, or soemthing.

WTF is a wonderful place to play. It is a safe, friendly, and imaginative environment for children and adults to enjoy. Because WTF is so much fun, it can be difficult to limit your time on the computer. Here are some tips about how to limit your time:
Use WTF as a reward. You will be able to play in WTF AFTER you have finished homework, done a few chores, etc.
Decide what you believe is an appropriate amount of time for you to be on the computer and discuss it. Set a timer, if need be. When the timer goes off, so does the computer.
Do things that you enjoy, besides computer. Read a good book. Draw. Make a scrapbook. Write in a journal. Go to sleep. Parties.
There was so many ways. How can't you not find one?