Files changed on my website

Hi everyone,

I created my first website and I am using Ithemes security plugin for the first time. I am a complete newbie so I am sorry if this question has already been answered.

The plugin notified me this morning about some file changes on my website. I haven’t made those changes, they were made by an IP address located in Bulgaria. What should I do to protect my website and cancel those changes ? I don’t know how to do it and I can’t find any documentation about this kind of situation.

Thank you for your help