You can use interactive rebase. The answer from this post gives you an example:
How to change the commit author for one specific commit?.
In particular, you can do the following to change one specific commit:
git commit --amend --author="Author Name <email@address.com>" --no-edit
The author asks for changing author at a specific commit, but interactive rebasing can be used to change authors of multiple commits if you edit all commits that you wish to change.
Other potential useful techniques related to interactive rebasing could be found in the Pro Git book
http://git-scm.com/book/en/Git-Tools-Rewriting-History, including squashing, redordering, editing messages, etc.