I also need to know if there is place in the airport to exchange currency
Also, how much taxi usually take from airport to city center
I think you mean to Old City - it will be 12 to 14,000 pesos and a very quick ride. Taxi's are easy to take from the airport with an official dispatch point.
There is a currency exchange at the international arrives.
Taxis are around $COP15.000 (5 dollars) to the Historical center.