Regardless of whether you see a premium increase or decrease, you should absolutely renew your flood insurance policy if your home is at risk for flooding. In some cases, it may be mandatory. Federal law requires it if your home is in a high-risk flood area or a Special Flood Hazard Area. Even if the feds don't require it, your lender may, if it is uncomfortable with the flood risk of your home, require flood insurance.
Even if it isn't required, you should consider renewing your policy. Flood damage can happen quickly and be shockingly expensive to repair. A standard homeowner policy does not cover water damage due to flooding, so if your home is severely damaged or destroyed after a flood, you will be on the hook for those costs.
Flood insurance policies take 30 days to take effect. If you let your policy lapse, you will be without coverage for at least 30 days while you wait for a new policy to provide coverage.