How to increase password length while creating account on a drupal website?
Sounds as if you need the Password Policy module.

From the project page:


  This module provides a way to enforce restrictions on user passwords by defining password policies.
  A password policy can be defined with a set of constraints which must be met before a user password change will be accepted. Each constraint has a parameter allowing for the minimum number of valid conditions which must be met before the constraint is satisfied.