Usually the update process on pihole is very simple: you just run the command pihole up.

When you don’t update it constantly, it can happen that you obtain some message like the following:

Here your local repository has gone out of sync with the master repository at github. To fix, you just have to run the following commands:

  cd /var/www/html/admin
  sudo git fetch –tags
  sudo git reset –hard

You could still get errors like: fatal: Unable to create ‘/var/www/html/admin/.git/index.lock’: File exists. In this case consider removing the index.lock file, after stopping the involved process if necessary.

Finally go with:

pihole -up

Happy update!

Source