Aurelio,
Lots of comments there that go both ways. If you still plan on doing it yourself (my vote) spend the extra $20 to get the little yellow plug tester. It has three little lights on it that light up and tells you if you're right or wrong.
Key note - plug it in first and check your circuit. If you have an existing problem - fix it while replacing the new outlet or before replacing the new outlet. If the two correct lights are on - make the new one just like it.
I say this because it helps you in two ways. One you see that it's on and when it's off (positive confirmation) - you're safe when it's off. The second, if there is a problem currently, you don't question if you did it or not. May not seem like a big deal - but if you just swap it and find a problem afterwards, you don't know if the problem is caused by you at that outlet or if the feed line has an existing problem.
Of course - if there are any problems - you should address it with an electrician before attempting anything. The kind of problems you can find is reverse polarization, shorts, open-grounds etc... They'll likely charge you more to come in and find an opened outlet and have to fix it because they are taking a risk that you've been in the wiring and their work would be blamed if anything goes wrong.
Steve Beckham
Epilog Mini 24 with 45 Watt, Ricoh GX 7000 Sublimation, Corel X3, Corel X4 and PhotoGrav, Recently replaced the two 'used' SWF machines with brand new Barudans.