Your modifications are in a different branch than the original branch, which simplifies stuff because you get updates in one branch, and your work is in another branch.
Assuming the original branch is named master, which the case in 99% of git repos, you have to fetch the state of origin, and merge origin/master updates into your local master:
git fetch origin
git checkout master
git merge origin/master
To switch to your branch, just do
git checkout branch1