You can read higher voltages, but you will need another resistor, to create a voltage divider.

Wikipedia has a good page on resistor voltage dividers. You want the intro and general case sections.

What that page doesn't tell you is what resistance to start with. Basically, you want to minimize the current flowing into the Arduino. I like to start generally with 10KOhms for the bottom (ground side) resistor, and then calculate the other one from that, hoping it matches closely to a standard resistor value.

This page has an excellent voltage divider calculator. However, it does not match it to common resistor values. I ran it for a 6.6V max input, and then compared it to common values and came up with a 3.3KOhm and 10KOhm resistor, with the 10K connected to ground.