Upgrade membership

How do I sign up for a Premium Membership?
What memberships are available?
I'd like to sign up to XING ProJobs. What will happen to my Premium membership?
I would like to become a XING ProBusiness member. What will happen to my Premium membership?
What happens if I want to purchase XING ProBusiness as a basic member?
As a company, can we acquire Premium licences for our employees?