Hi,
1. For this you will need to develop custom functionality to store the cred card details - Kentico
CMS is not storing any information like this and due to security it is up to you to implement this to allow automatic charges.
2. You mean during the membership or just if their membership is about to expire? The user can still purchase to upper or lower level of your membership anytime. I am not sure how exactly you want the behavior to be.
Best regards,
Juraj Ondrus