If you have a version of Office that has Microsoft Office Picture Manager
(MOPM), converting from jpg to tiff is quite simple. Open the picture using
MOPM, then choose File - Export, and set the Export... format to TIFF.
Whether that will improve the printing of a grainy picture, however, I can't
say... I'd be surprised if it does, since changing from jpg to tiff isn't
going to magically improve the picture quality.