Before I mention the steps, here's a tip if you want to save your current branch's state:
git commit -a -m "Saving my work in my-saved-work branch"
git branch my-saved-work
Now let us set our branch to exactly match the remote branch:
git fetch origin
git reset --hard origin/master
Here, the remote repository named "origin" and that the branch named "master" in the remote repository matches the currently checked-out branch in your local repository.
Now addressing your next query, to remove those untracked files, use the following commands. But before performing clean take a look at the files that will be cleaned.
git clean -n -f
Now if you think these files add no value and can be removed, use the following command:
git clean -f
For more information please go through the following tutorial to get more info about git: