A seguir a sequências de comando para atualizar um repositório fork a a partir das mudanças originais.

$ git remote add upstream https://github.com/opencv/opencv
$ git fetch upstream
remote: Counting objects: 53, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 53 (delta 40), reused 41 (delta 40), pack-reused 10
Unpacking objects: 100% (53/53), done.
From https://github.com/opencv/opencv
 * [new branch] 2.4 -> upstream/2.4
 * [new branch] master -> upstream/master

$ git checkout master
Already on 'master'
Your branch is ahead of 'origin/master' by 237 commits.
 (use "git push" to publish your local commits)

$ git rebase upstream/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to upstream/master.

 
Caso deseje remover o upstream

$ git remote add upstream https://github.com/opencv/opencv