First use
git log
to find the change ID you want to revert back to.
Note that
git reset
will keep your changes unless you specify the --hard option
#Reset back to given ID (only removes commit information, keeps file changes)
git reset ID
#Now re-add and commit them
git add file1
git add file2
git commit
#Now push your changes to the master
git push origin HEAD:refs/for/master
NOTE: If you want to scrub everything and reset to a given level (both files and commit logs) then use
git reset --hard ID