The rules for changing your password are as follows:

• Must begin with a letter
• Minimum 12 characters, Maximum 30 characters
• Must use at least 3 of the following 4:
  
  • An UPPERCASE letter (ABCDEFGHIJKLMNOPQRSTUVWXYZ)
  • A lowercase letter (abcdefghijklmnopqrstuvwxyz)
  • A number (0123456789)
  • A special character (! @ # $ % ^ & * - _ + = [ ] { } | \ : ' , . ? / ` ~ " < > ( ) ; are allowed)

Please refer to this article for assistance in creating a strong password.