Malware – akciopalota.hu

I need help please. I cannot even access my dashboard. I do not know how to get the malware off if I cannot access anything. I am not good at code, I have installed a theme and have no idea how the website suddenly got hacked after years of using the theme. I have no idea what happened or why this is suddenly an issue. Someone please help!

Website is rmga.org, not that it will help anyone since it brings up a malware warning screen. But on a smart phone it is some ad for a sweepstakes.