Replacing is straightforward. See ChrisF for the details.
However, I just wanted to add the following (Since you appear to be from Wisconsin, I'll assume 120v 60hz wiring) :
1: Standard wiring for an outlet is
- Black wire - Gold coloured screw.
- White wire - Silver screw
- Bare or green - Green screw
(usually connected to the metal
Get a three pronged wiring tester and test the wiring BEFORE removing the outlets. Put a post-it on any that doesn't test properly. That way, you'll know to check it when you're wiring.
Three things you need to watch for:
Chained outlets - This occurs when there are two blacks attached to the hot (gold) terminals. They may be attached to the same screw or a different one on the same side. What is happening, is the hot is being carried over to another outlet or to a switch on the same wall. (same for white) - rewire the same way. BUT - Make sure it isn't a SPLIT!
SPLIT outlets - These are most common in the kitchen. There should be two blacks to separate terminals, two whites (also to separate terms) and two greens (to same terminal). The difference here is that there is a small knock-out removed between the screws that electrically separates the upper and lower receptacle. This allows you to wire each receptacle to different circuits, allowing you to plug in the toaster and the kettle at the same time without tripping the breaker. When buying receptacles, ask the hardware guy to show you where the knockout is, and when you remove the old one, check for a split. -- Edit based on comment to another answer: Beware of splits because one outlet may be de-activated at the breaker, but the other could still be live. Always check both outlets before opening.
Switched outlets - These usually are splits, with one receptacle wired black & white (always on) and the other wired red or blue and white. The red wire is a switched hot, coming from a wall switch. The knockout should be removed, but they may not be on separate circuits. If they are on the same circuit, they will often only have a single white on the neutral side, and the knockout on the neutral side will not be removed.
If you come across any other creative wiring, call an electrician to sort it out.