Setting your branch to exactly match the remote branch can be done in two steps:
git fetch origin
git reset --hard origin/master
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
If you want to remove local files to have an exact copy of remote branch you do:
git clean -ffdx
To see what files will be removed (without actually removing them):
git clean -n -ffdx