Setting your branch to exactly match the remote branch can be done in two steps:
git fetch origin
git reset --hard origin/master
Update @2020 (if you have main branch instead of master in remote repo)
git fetch origin
git reset --hard origin/main
If you want to save your current branch's state before doing this (just in case), you can do:
git commit -a -m "Saving my work, just in case"
git branch my-saved-work
Now your work is saved on the branch "my-saved-work" in case you decide you want it back (or want to look at it later or diff it against your updated branch).
Note that the first example assumes that the remote repo's name is "origin" and that the branch named "master" in the remote repo matches the currently checked-out branch in your local repo.
