photoshop question

Say I have an image-- something fairly small, computer-drawn, basic colors, with clean solid lines. I want it to be bigger, so I enlarge the image size, and then the nice lines are all bumpy and pixelated looking because they were diagonal or curved or whatever.

Is there anything in photoshop that can make an educated guess at what the lines ought to be and smooth them out without my having to do it pixel by pixel? I feel that "this formerly appeared to be a perfect circle" ought to be within the capabilities of modern drawing programs.

am I asking too much?