I received notification about needing to renew my Ascendant membership via email. In that email, the instructions were as follows:

To update your billing information, please log in to obsidianportal.com and go to your user profile. From there, click on the Membership tab and then click the Update your payment details link.

If you follow those steps, you won't find the membership link. Aside from going through a separate payment (which I have already done in this case), how would someone update their membership information?