How to convert png pictures to jpeg on windows 7?

I emailed pictures off my iPhone to my email and saved them on my computer and now I can't print them on walmart and i'm thinking its because of the reason above. I'm new to the latest version of windows so if someone could help that would be awesome

Open image with paint. File< Save as< select the extension you want.

You should download the free program irfanview. Open the png picture and save as jpeg. I use this program since the beginning of time! Paint will not give you options for transparency and quality.

Just about any program you open them with can save a copy as a jpeg. You usually just click on "file" and "save as".