Best way to convert mutiple Bitmap files to Jpeg

Could you please recommend a software (preferably freeware) that can open up multiples Bitmap pictures then convert and save as jpeg files. Of course, I can open one by one, then “save as”; but any shortcut? I am trying to save my hard drive space.

Thanks in advance.

Thank you MetalSlayerX , I have tried it out and works as expected.

http://www.imagemagick.org/script/index.php
//Danne