Vantage Theme problem

Hi all. I am using the Vantage theme I noticed this morning while checking my website that something had changed overnight. On all my pages my custom logo which was once small and in the menu bar, is now massive and above the menu bar. This literally changed overnight because I checked the site yesterday and it was fine. My website recently updated to version 4.2.1 of wordpress but that was 3 days ago and I didnt have this problem until today. Any thoughts or suggestions? Please keep answers basic as I am a novice at this. Thanks in advance.