Here is short summery of how to change password requirement in AD environment.
First go to run and type gpmc.msc or go through admin tool and group policy.
I would highly recommend starting a new GP. It is not a good practise to tinker around default GP.
Then go to Computer configuration—> Policies—->Windows Settings—>Security Settings—>account Policies and then Password policy.
There are many things that can be enable, so you can force users you complex password instead using simple 123 password 🙂
You can also find similar config this under local PC local security policy and account policies and password policy.