If I downgrade to a free account will I lose all stored information?

No. All stored data will remain.

The only time data will be lost is if they were deleted.

In certain situation, you may not be able to access the data of the downgraded account become in Overlimit Status.

Meaning, if its a FREE account, and the data on the form exceeds the limits allowed for the FREE account (i.e. PREMIUM have higher limit than FREE)

Let us know if you need further assistance.