This file contains method to uncommit files and message and simply uncommit a message

uncommit.md

to uncommit all the stuff: both the message and added files:
git reset HEAD~

in this case you would have to add files and add message before making commit.(changed and added files(staged) are unstaged).

if just just want to edit message of the commit then use soft HEAD:
git reset --soft HEAD~

to reset to a particlar commit :
git reset --hard 4a155e5