Evilution is a fantastic site for all things smart related in the repair department.it covers not only the early smarts (450 models) but everything up to the 453 models. It is privately owned and subscribing is not at all expensive and helps support the site.
Only downside I've seen currently in regards to evilution is that info for the 453 is scarce at the moment... with resetting the service indicator being one of those instances.
All you have to do is scroll down (or up) through the instrument panel screens til you get to the service interval screen where it'll tell you how far you have left or how far you've gone over... not sure if it matters whether or not the car is actually running, or if just having the key in the accessories position works, too. Then just hold the OK button until it resets. Have to hold it in for a good long while, too. IIRC, when you first press and hold it, it'll seem like nothing is happening for a while. Then I believe it starts flashing on the screen. After a couple seconds of flashing, it'll reset. Not 100% sure on exactly what happens as you're holding the button, all i can remember is that it takes a bit longer than you'd think it would. Guess they REALLY want to make sure it's not "accidentally" reset.
Oh, and if you're talking about changing the oil yourself... I'd highly recommend using ramps if you have them to park the back end of the car on.... or go buy some.... or use a lift if you have one. Don't do what i did and rely on a floor jack. Where the oil filter is located can be a royal pain to reach... and I have long arms.