Fixing commits

This is mostly from here.

Fixing the last commit

Changing the last commit message

git commit --amend -m "New message"

Changing the last commit

Make your changes to the files
Run git add <filename> to add one file or git add <filename1> <filename2> ... to add multiple files
git commit --amend

Fixing older commits

Changing commit messages

git rebase -i HEAD~5 (if, for example, you are editing some of the last five commits)
For each commit that you want to change the message, change pick to reword, and save
Change the commit messages

Deleting old commits

git rebase -i HEAD~n where n is the number of commits you are looking at
For each commit that you want to delete, change pick to drop, and save

Squashing commits

Sometimes, you want to make one commit out of a bunch of commits. To do this,

git rebase -i HEAD~n where n is the number of commits you are interested in
Change pick to squash on the lines containing the commits you want to squash and save

Reordering commits

git rebase -i HEAD~n where n is the number of commits you are interested in
Reorder the lines containing the commits and save

Pushing commits after tidying them

git push origin +my-feature-branch (Note the + there and substitute your actual branch name.)