Current salary/ salary expectations during the interview

How would you reply when asked about your current salary/ salary expectations during an interview? Im afraid of being low-balled if I'm honest. the reason being is with my first job I was paid a diploma salary. for my 2nd job after I finished my part time uni, I had a 15% increase annual but it just puts me on the lower end of the degree holder salary since my 2nd company offered me based on my last drawn diploma salary. any advice would be greatly appreciated. thank you :)