If you think you have a puncture whilst driving along it is advisable to pull over as soon as possible. Having a flat tyre can make it difficult to control the vehicle the car can pull to one side and may become more difficult to steer.
If you are in a safe enough space to change the tyre yourself do so otherwise call your breakdown assistance. If you are going to change the tyre yourself make sure you have the necessary controls such as a spare tyre, a jack, vehicle handbook to tell you the jacking points of the car.
A flat tyre doesn’t always mean you will need a new tyre. A flat tyre mainly occurs when you have a puncture. A simple puncture can be fixed, however, if a tyre is driven on whilst it is flat the sidewalls can rupture and can unfixable damage to the tyre meaning it will have to be replaced.
To avoid a flat tyre ensure your tyres are properly inflated and try and get into good driving habits to prolong the life of your tyres.