The OP is being offered a bigger tire, 5-series sizing to be specific. So a wider and taller tire. Not best for winter, I'm taking 245 sections off my car and fitting 225 section tires for winter use.
Going wider for winter is not the best idea, even if the taller tire has space. Also remember it will change the speedometer to 'real speed' accuracy, due to larger rolling circumference.
BTW, the '45' is an "aspect ratio", just as mikew has highlighted.