Enlarging a photo

Hi,

 I think you first have to scan the film into digital media,

the better scanner you have, the better will be the result. 

then, you can use a wide range of software capable of enlarging photos from small size to a bigger size.

I used (with my digital camera) a software called "Genuine Fractals", this software comes as a plugin for photoshop, and  it does the work very well , if you are not over sizing.

It depends on how large is the print you want to scan for the purpose. Even if you intend to scan a negative. you should try and scan it a the highest quality available.

I assume that a normal 10X15 (cm) image could be resized 3-4 times bigger which will bring it to about A4 size. try enlarging it in photshop, and see what you get.

You can also try and use  dedicated software (like Genuine Fractals) I also suggest reading here as well.

You should bring the negative to your photo finisher. Film resolution depends on the grain so if you are enlarging from 35mm you will start seeing a grainy picture if it is enlarged too much.