Getting a puncture on the move can be quite scary, but try to keep calm. The safety of you and your passengers is the most important thing. Here's what you should do:
1) Find a safe place to pull over. Make sure you put the handbrake on.
2) Switch off the engine, keeping the car in a low gear.
3) Switch on your hazard lights.
4) If you have a reflective vest, put it on.
5) Place your warning triangle at the side of the road approximately 100m behind the car.
At this point you'll need to decide whether it is safe to change the tyre – if you have one that is. Make sure you check whether you have a puncture repair kit, a space saver or a full size spare so that you’re prepared should you ever get a puncture.
If you're on the side of the motorway or a busy road then don’t attempt it. You'll then need to get everyone out of the car and to safety (which might be up the top of the motorway verge). Assuming it’s safe to continue and you know what you’re doing:
1) Equip yourself with your gloves, user handbook, jack, spare tyre, wheel chock (wedge) and a wheel wrench. Make sure you read the instructions in the handbook carefully before you start.
2) Ensure everyone is out of the car.
3) Remove the wheel trim if applicable.
4) Place the jack on the car's jack head, as per your handbook (don't put it anywhere else) and start to turn the handle until you feel the car lift very slightly.
5) Loosen the wheel nuts, but don’t remove them yet.
6) Carefully raise the car so it's just clear of the ground.
7) Remove all wheel nuts apart from the top one. You'll need to balance the wheel on the hub with your knee or toe. Once you've removed the top nut lift the wheel away.
8) Now fit the spare, doing the reverse of the above. Ensuring that you have tightened the nuts sufficiently.
You should always visit a garage to have the punctured tyre replaced and fitted professionally. Don't just leave your spare tyre on as you'll obviously not have a 'spare' anymore. If you’re worried about tyre changing, you can always call a breakdown service such as the AA, the RAC or Green Flag to come and help you.