How to merge remote changes at GitHub?
See the 'non-fast forward' section of 'git push --help' for details.
You can perform "git pull", resolve potential conflicts, and "git push" the result. A "git pull" will create a merge commit C between commits A and B.
Alternatively, you can rebase your change between X and B on top of A, with "git pull --rebase", and push the result back. The rebase will create a new commit D that builds the change between X and B on top of A.
You can also force a push by adding the + symbol before your branch name.
git push origin +some_branch