Is it possible to actually stop your premium subscription instead of just stopping renewal?

I am going to upgrade to a higher tier of Premium, but I have to wait until my subscription expires. Do I have to wait until it expires, or is it possible to actually stop it?

According to the forums and the help pages, it looks like the answer to your question is yes, you will have to wait until it actually expiries before upgrading. The information looks consistent across the site as well, as this help page states the same info.

Forum:

Help - Upgrade or Downgrade Membership:

Help - Premium Membership:

I suggest cancelling it now as to avoid the hassle of forgetting and having to wait another month.