Maintenance can be several things. It could be an oil change (you had done), it could be coolant flush, it could be tune-up. It just depends on how sophisticated your cars' system is.
The maintenance light must be manually reset by simply depressing the small black button directly next to the indicator. It operates mechanically off of the odometer, and is incapable of sensing things like oil condition etc. and is meant as more of a reminder. Just reset and you'll be good!
:EDIT:
Sorry, I was mistaken, and was thinking these cars shared the same instrument cluster as a Honda (Civic, Accord, etc...) Apparently the button is at the bottom of the knee bolster, on the accelerator side. Here's a quick video I found on YouTube...