Can't Login – Loading as HTTPS not HTTP?

Hi! I would be really, really grateful if someone could help me out with this. I’ve been trying to login to my self hosted wordpress site for days (www.swimminginsunshine.com), but whenever I do, the url shows HTTPS in red with a little slash through it, and I get this error message:

Your connection is not private

Attackers might be trying to steal your information from swimminginsunshine.com (for example, passwords, messages, or credit cards). NET::ERR_CERT_COMMON_NAME_INVALID

What I can gather from reading online is somehow my site is being categorized as HTTPS when it needs to be HTTP, and I need to somehow edit my functions.php, but how can I do that if I can’t login??

Thanks!