My project is to find latitude and longitude of certain places. I am using an Arduino Uno R3 with a Cytron GPS 53 shield to get the position of places but, my device cannot run because COM4 already in use. How to fix this error?
Your GPS board supports sending the data to the USB socket on the Arduino, sending it to pins 0 and 1, or sending it to a Software Serial port. The first two options are going to confuse the output you are getting from the Arduino, so you should probably use the Software Serial option (read the manual on how to do that).
The data that you receive on the Arduino from the software serial port will need forwarding to the USB serial port that your PC is connected to, you will have to right a program to do this, but its not a difficult program and I'm sure there are examples out there.
If you want to make this mobile, you will need a battery to power the kit and an LCD display to show your results (get one with an I2C 'backpack' it will be easier to program).
Hopefully that should give you a start.