How to order plans for upgrades

Hi there, I have been running your membership plug in for a few weeks and I have found a small problem that I think it a configuration problem?
I have 1 membership and 2 subscription plans - one subscription is for 7 days (trial) and the other is for 1 year (full membership)
If a user has a full membership and views their current subscription they have the option to "upgrade" to the 7 day trial - this is obviously wrong...
What have I done wrong and how do I fix it?