If you downgrade to a plan that supports fewer social accounts than you currently have connected, any social accounts above the limits of your new plan will become locked. We would recommend removing any social accounts that you no longer need, which will then unlock the social accounts you're looking to keep.
If you'd rather not delete any social accounts (for example, if you would like to keep them connected in case you upgrade again in the future), you can choose which social accounts to unlock using drag and drop. Drag the social accounts you'd like to unlock to the top of the list on the left hand side of your dashboard. The social accounts nearest the top will unlock and the accounts nearest the bottom will lock.