FORD1972

Hello all I am very new to photo editing and I just downloaded paint .net and am clueless. Here is what I am attempting I have a picture that I made on Windows paint and I wish to have labels made of it via Vista print or maybe Kinkos not sure yet dont like the Vista print shipping price to good. The picture I upload must be at 300 DPI how in thhe Paint.net program do I physicaly change the DPI ? Also how do I set the size to around 3"x4"?I mean where in the program do I go to set these things? Once again Ime very new to photo editing can anyone grab me by the hand. Thank you. + +