overwrite other branch(github) in Smartgit

You can reset your local new branch to master, then force push it.
An example of reset with SmartGit is seen here.

Even without smartGit, you can do that in command-line:

cd /path/to/my/repo git checkout master git pull git checkout newBranch git reset --hard master git push --force -u origin newBranch 

However, as the OP comments:

This reset deletes github commits and copy master to other branch.
Namely I want to commit all master code to other branch in github and I don't want to delete past commits

In that case, you can:

• find the commit that newBranch was referencing before being reset: see "Recover from git reset --hard?"

That is:

git checkout newBranch git reflog show git reset --hard <oldSHA1 of newBranch> 

• checkout the files from master (while staying in newBranch)

  git checkout newBranch git checkout master -- . 

(note the final -- .: "dash-dash-space-dot" at the end of the second checkout)

• add, commit and push: you will add, commit and push files from master in newBranch, while keeping the history of newBranch.
  If you had already pushed newBranch before, you will need to force the push

  git push --force