I have two working branches, master and forum and I\'ve just made some modifications in forum branch, that I\'d like to ch
Run git gui, select the "Amend last commit" radio button, and unstage (Commit > Unstage From Commit, or Ctrl-U) changes that you do not want to go into first commit. I think that's the easiest way to go about it.
Another thing you could do is cherry-pick the change without committing (git cherry-pick -n) and then either manually or with git gui select desired changes before committing.