What to do with a child  o f    8    years old with behavioral problems?

More Info Needed. The term "behavioral problems is s very broad category so it's hard to give specific advice. However, if there has been a recent change in the child's behavior it's always a good idea to talk to your primary care doctor to make sure there is not some physical problem. Also, check to see if something in your environment is contributing to the behavior problems.
A good book. Buy and read the kindle book: parenting the kids according to a child psychiatrist. It is only $5.95, you can read it in about one hour. It will make a big difference.
Start with... A good start might be to consult with your pediatrician to perhaps define the problem and begin work to help correct it. Specialists may be needed, but sometimes a beginning is necessary.
Always difficult. Children respond to loving guidance better than punitive measures. You should reserve strong language and physical actions for activity which might be dangerous. Otherwise you have a difficult challenge. Discuss with your pediatrician whether there is a physical cause. And then get recommendations for behavioral therapy which is a whole family problem. Good luck.