Reverting commit changes from HEAD

# we have a change
ronen@Lunar:~/dummy$ gits
# On branch master
# Changed but not updated:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#
#	modified:   bla
#
no changes added to commit (use "git add" and/or "git commit -a")
ronen@Lunar:~/dummy$ gitc 'added a wrong change'
[master 14af00a] added a wrong change
 1 files changed, 1 insertions(+), 0 deletions(-)
ronen@Lunar:~/dummy$ gits
# On branch master
nothing to commit (working directory clean)
 
# weve made a bad commit
ronen@Lunar:~/dummy$ cat bla 
initial value
wrong change to make
# lets fix that (we replace it with an empty line
ronen@Lunar:~/dummy$ vi bla 
ronen@Lunar:~/dummy$ cat bla 
initial value
                        <-- this is an empty line!
ronen@Lunar:~/dummy git commit --amend bla