How to squash commits into one

1. use git log --online to check all your commits history in a brief form.

2. find the hash head of the first commit you want to squash to.

3. run git reset --soft <hash> to reset the HEAD to that commit.

4. run git add . to add all the changes made in commits after the first one.

5. run git commit --amend -m "new commit message" to replace the old commit message in the first commit to the new one.

   ATTENTION: In step 5, omitting --amend would result in making a new commit and squash all commits into that new one instead of the first one.

6. run git push --force