Increasing the range of XBee Pro S2C

I have 2 Xbee’s (XBee Pro S2C). First XBee is Coordinator and 2nd Xbee is Router.
2nd Xbee(Router) is connected to Arduino(GPS is connected to Arduino) to send GPS data to my coordinator XBee.
Coordinator XBee is connected to my PC. I will check GPS data through X-CTU.
But the problem is range. I need 5km range.But range of XBee S2C is 3km currently. How could I increase the range of Xbee(5 km range)? What type of antenna I should prefer?
How can I remove the other antenna? What happens if I implement 900 MHz antenna instead of 2.4 GHz antenna?

You are going to need to use a higher gain antenna. The problem is, you may not be allowed to. That is determined by your local regulations.

The ability to change the antenna is dependent on what version of the module you have. If this is the U.FL or RPSMA version, then it is simply a matter of using a higher gain antennas (at least 6db more in gain) in the same 2.4 GHz band.

As for using a 900 MHz with a 2.4 GHz product, it is not recommended. The antenna is tuned to a specific frequency range. Using an antenna that has been tuned for a different frequency can cause issues.