Installing a new battery is not a difficult job, if you know how. And knowing how can save both time and money.
The first step is to disconnect the negative cable from the battery. There are three kinds of connections commonly used:
1. Spring-type clamp. To remove a cable with a spring clamp, squeeze the clamp's "ears" together with piers, rotate the clamp back and forth to break it free from the battery post and lift.
2. Bolt-and-nut clamp. This type of connection is used on batteries with upright posts. To remove it, you place a wrench on the bolt, then loosen the nut with another wrench. It's best to use a box-end wrench when loosening the nut -- this reduces the chances of rounding off the nut. After the nut is loose, lift the clamp off the battery post, with a cable puller (not expensive, lasts indefinitely, and available at autoparts stores and the like) or, if you don't have a cabel puller, by hand. Try to rotate the cable back and forth to break it loose, then lift it off. If it's frozen and you can't rotate it, stick a screwdriver blade between the clamp's two "ears" and pry the clamp apart slightly to break it loose. Then rotate it back and forth with your hands and lift it off. (Never stick a screwdriver under the clamp and pry up; you can break the battery terminal this way.)
3. Side terminal clamp. With this type you just remove the bolt and lift the cable away.
Okay, back to that negative cable. It will be black, and at the battery terminal area you'll see the letters "NGE," a minus sign, or both. Loosen the clamp and remove it from the battery.
Then disconnect the positive cable -- it's the remaining cable, and it will be red, and at the battery terminal area you'll see a plus sign or the letters "POS" or both.
The battery will have a hold-down to keep it from falling out of its box. The hold-down is often held in place by a couple of nuts. Remove the hold-down. Now you're ready to lift the battery out.
Remove the battery.
Now place the new battery in the battery box. Be sure that when you put it in place the positive and negative terminals are in the same position as the old battery. Then replace the battery hold-down and tighten it -- not super-tight, just enough to keep the battery from bouncing around as the car travels. Now replace the positive cable, then the negative cable.
Afterward, it's not a bad idea to coat the outside of each connection with a light coating of vaseline. This helps deter corrosion buildup at the terminal connections.