At some point it will happen (usually at 1AM on Sunday). Your water heater will go "kaput". This is a "technical" plumbing term that means the water heater stops working for good.
Water heaters are supposed to have periodic maintenance but all too often they are just left to churn away without maintenance and thanklessly make hot water for us, day in and day out. When they've had enough, they quit due to rust and corrosion.
The quickest and easiest way to replace a water heater is to have it done by a plumbing professional, but if you can't afford it or really want to do this yourself, then read on. You need to make sure you're following plumbing codes so calling your local plumbing inspector to find out what municipal permitting requirements and specific criteria they may have is a good idea. But replacing a water heater is not extremely hard, and if you follow this tutorial you'll be back in hot water in no time. Well, plan on a good 4 to 6 hours anyway.
Selecting Your New Water Heater
When selecting your new water heater it's easiest to keep the same fuel type, whether gas or electric. That is the assumption made in this tutorial, that you'll keep the same fuel type as the water heater you're replacing. You can change the size a bit however. For example, let's say you had a 40 gallon and want to go to a 50 gallon. That should not be a problem as long as you have clearance between the heater and the wall.