The battery is on the left side of the engine compartment.

The cable connecting to the negative terminal should be black, and should have an exposed 8mm bolt head that screws into the battery. The negative terminal should also be marked on the battery.

Use an 8mm wrench to disconnect the negative terminal connector. Tuck the lose connector out of the way of the battery, so that it cannot make contact with the terminal.

Be very careful not to touch the positive battery terminal (with the wrench or yourself) while you're doing this. There should be a red protective cover on the positive terminal, but it's always good to take precautions. Shorting out a car battery will very likely result in a trip to the hospital.

New batteries tend to come with plastic plugs for the terminals. If you have these for your battery, this would be a good opportunity to use them. This will prevent anything from touching the terminal.