It's always good to keep an eye on your vehicle's health, and to know some basic skills of looking after your car, as you can't rely on a 24 hour break down service when you are off grid and miles from civilisation.
Changing a wheel:
Turn the engine off and put the hand break on. If you're on a slope find something to chock the wheels so it can't move. In the boot there should be a spare wheel, a wheel-nut wrench (with a special adapter if your wheels have 'locking' wheel nuts) and a jack. Remove them all and lay the spare tyre on the ground next to the flat one. Lever off the wheel trim or hub cap on the flat tyre so you can get to the wheel nuts.
Your vehicle handbook will show you where the jack needs to be positioned. Don't put it just anywhere – you'll damage the vehicle and get yourself into more trouble. Use the wrench to crack the wheel nuts loose, but don't fully remove them yet. (You may need to use the locking wheel-nut adapter for one of them.)
Now, raise the jack so the vehicle is just off the ground. You don't want it to be sky high, but it needs to be high enough to allow the more inflated spare tyre to fit on. Remove the nuts, leaving the top one till last. Place them in a secure, clear place. Now remove the wheel. Reverse this procedure to fit the spare. Tighten the nuts by hand first, using a diagonal pattern, then tighten them to a pinch using the wrench. Lower the jack so the wheel sits on the ground. Finish by fully tightening the nuts using the wrench, again in a diagonal pattern. Remember, never put yourself under the car when its supported by the jack.
If your cars' battery is dead, you can jump start it from another cars' battery. You'll need a set of jump leads. Put both vehicles in park and turn the ignition off. Attach one of the red jump lead clips to the positive terminal of the working battery (it will have a + sign or the letters 'POS'). Then attach the other red clip to the positive terminal of the dead battery and attach a black clip to the negative terminal of the working battery (it will have a – sign or the letters 'NEG'). The other black clip attaches to a good earth, such as an exposed bolt-head or designated earthing point (look for a label with an earth symbol, or an exposed copper bolt-head). There may be a little sparking so always use the designated earthing point or a suitable earth away from obvious sources of ignition. Turn the ignition on in the car with the good battery, leave for a few minutes and then try the car with the flat battery. Once it starts remove all the cables and drive the car around for at least 15 mins to charge the battery.