To reset the default password policy in Active Directory you should follow the steps below:

1. Open the Server Manager console.
2. Navigate to the Tools tab and select Group Policy Management.
3. Select the Default Domain Policy under the Domain Policies folder.
4. Edit the policy.
5. Under Computer Configuration > Windows Settings > Security Settings > Account Policies > Password Policy you will find the policy settings.
6. From here you can edit the desired settings.