I bought a refurbish macbook air,mid 2012. Upper key and cover is getting hot. It seems that average temperature is 60c with fan speed rpm 2,000. How I can have temp less than 45c?

Believe it or not, the internal temperature can reach the boiling point of water. What you really need to worry about is if the machine decides to unexpectedly shut itself down. Consider the surface you have the machine on, and whether or not you are exceeding external specs for temperature. See this tip:

kmb kmbp: How to deal with MacBook Pro and MacBook heat?

I'd try resetting the SMC - Resetting the System Management Controller (SMC) on your Mac - Apple Support

If it still fails to lower the temperatures, bring it to the Apple store or call Apple. If it's not working the way you feel is right, bring it in - Use that Applecare!

Then again, just from my experience, that's hot but not anywhere near where you need to worry - 90-100C is when you want to worry. And your fan should start spinning much faster the hotter it gets. If the fan is staying at 2,000 rpm, the SMC reset should fix that.

I think the T-Max, or maximum running temperature, on the i-series CPUs is 105C ( at which point the CPU will slow itself down, or throttle, to protect itself so don't worry about melting it ). Good Luck!