You can order the Michelin Pilot Sport 5 235/45 ZR19 (99Y) XL and Goodyear Eagle F1 Asymmetric 6 235/45 R19 99Y XL at Tyres.co.uk for your GLA45 AMG's stock 19-inch wheels. Only the GLA45 AMG has these factory fitments. Before you check out, make sure to check both the registration and the fuel flap for fitment.
There is a sticker on the fuel filler flap of the Mercedes GLA45 AMG relating to tyres and tyre pressures. This defines the permitted tyres and pressures of the GLA45 AMG; it should be checked against the registration and tyre sidewalls.
The Mercedes GLA45 AMG doesn't always need four new tyres, but all variations use all-wheel drive: 4MATIC or 4MATIC+. These must be replaced in the same type and make, with matching dimensions. Tyres must be replaced in axle pairs; UK guidance is to fit the new pair on the rear axle.