Use the search tool above with your registration number for the correct match, or check the tyre sidewall and your door jamb/handbook for the exact size (for example width, profile and rim diameter) and then search by tyre size.
Many Boxster models can use Porsche-approved N-rated tyres (for example N0 or N1), which are tested to Porsche specifications; if you want to keep to approved fitments, filter for them after searching, and always match ratings across the same axle.
Summer tyres suit warmer months and spirited driving, winter tyres improve grip in cold conditions (typically below 7C), and all-season tyres are a compromise for mixed UK weather; your best choice depends on mileage, driving style and when you use the car.
You select a local fitting partner, choose an appointment slot, and the tyres are delivered to the garage for your visit; the fitter will install and dispose of the old tyres, and you should check tread depth (UK legal minimum is 1.6mm) and tyre pressures regularly afterwards.