Q: Can I use 60 W charger with MacBookAir?

you are fine  no worries.

from Apple

"Power adapters for Intel-based Apple notebooks are available in 45W, 60W, and 85W varieties. Although you should always use the proper wattage adapter for your Apple notebook, you can use an adapter of a higher wattage without issue."

Using an adapter of higher wattage than  the adapter that came with the computer will not cause the computer to  charge more quickly or otherwise operate any differently than using the  adapter that came with the computer.

http://support.apple.com/kb/HT2346

...and in that case, I'd buy the one Apple supplies the computer with just to be on the safe side, but since you already have the 60W and the manufacturer says it's OK to use, I wouldn't sweat it much if at all.