Hi I assume we are talking wheels, please observe the following, the difference in tyre widths and the fact that your car speedo is designed to run with 17 inch wheels so you will have to use really low profile tyres to get the total O/D of the 19inch wheels the same as the 17inch wheel or go to Audi to re program the body control to accommodate the new 19 inch wheels unless you are happy to drive around with a speedo that is not entirely accurate, your choice and I wish you well with it, if the roads are anything like the roads in Essex be prepared for an increase in punctures. The wheels should be a straight swap centre and stud wise, not sure if the offset will be different there is a website telling you which wheels will fit what models of Audi.
Steve.