You should periodically change the brake fluid in your vehicle; about every 30,000 miles is a good round number. The reason for this is because over time, brake fluid absorbs moisture and becomes acidic. This acid eats away at the internals of the brake system and can eventually cause a failure. In addition, as brake fluid ages, its boiling point gets lower. If your brake fluid boils, it can cause your brakes to fail. (I've never seen this happen on a street car; this would be a bigger concern on a race car or something like that.) Remember that brakes turn speed into heat. Your brake fluid has to deal with that heat. The newer the brake fluid, the better equipped it is to deal with that heat. To change your brake fluid is fairly simple. Just be sure to use the type of fluid your manufacturer calls for. It should be printed on the cap of the master cylinder or listed in the owners’ manual. Here's a video on changing brake fluid.