I'd be happy with this.
1. Login
2. Go to your account page.
3. That should have a link to billing management.
4. Somewhere on the billing management screen there should be some easy to figure out way to cancel.
Details will vary but in general cancelling logically makes the most sense as part of payment management, so it belongs where other payment management goes such as adding or updating a credit card.
If the site wants to it would be fine to have a separate subscription management section that is linked to on the account page parallel to billing management. That might make sense if it is a service where there are options users can add to or remove from subscriptions.
For example a streaming service might have separate paid options such as higher video resolution, more simultaneous streams allowed, removing ads, and adding specialized content (e.g., porn, foreign language videos).
That wouldn't really belong under billing so putting it in a separate subscription management section would be better, and then cancelling would best fit there too. Billing management would then just be managing your payment methods.