Howto? It's pretty easy.

Don't stand in water when doing it

Remove the negative battery terminal first. make sure that doesn't flip back and touch the terminal... that can be bad :rick:
Next remove the positive terminal. Remember that the whole ground and pretty much everything metal under the hood is negative/ground sooo it's generally a good idea not to touch anything AND the positive terminal at the same time.

Once those are both off... you will probably need to remove some sort of battery tie down. It's usually just 2 nuts or screws.

Lift the battery out, not by the terminals though. If it's got a battery cover around it, take that off and put it on the new one. Then just reverse the process. Battery in. Connect the positive. Then last the negative.