1. Login to ESXi console

  2. Go to Host > Manage > System > Advance Settings

  3. Search "Password"

  4. Select "Security.PasswordQualityControl"

  5. Action > Edit option
    vmware-002

  6. Change value as you perfer. Example: retry=3 min=1,1,1,1,1
    vmware-003

  7. Check for change.
    vmware-004

  8. Try to change password by go to Host > Manage > Security & Users > Users

  9. Select user "root" > Edit user
    vmware-005

  10. Change your password.
    vmware-006

  11. Set "Security.PasswordQualityControl" back to default value.

Reference:
http://vcdx56.com/2016/04/change-esxi-password-complexity-policy/
https://communities.vmware.com/thread/527843
https://www.perfectcloud.org/fix-it/vmware/disable-esxi-password-complexity/