And here's how to reset it if you can still reach the in­stal­la­tion via SSH or similar.

Start a Django shell:

python manage.py shell

Use the following code to change the password:

from django.contrib.auth.models import User
u = User.objects.get(username__exact='[username]')
u.set_password('[fill in new password here]')
u.save()
exit()

That's all!