Speed ​​change on open serial port

Question

Possible duplicate:
Change BaudRate SerialPort when opening a connection

I know how to open, close and configure the baud rate for a port, etc., but while the port is still open, I want to change the baud rate from 9600 to 115200.

I looked at it and he said that this can be done by issuing a command to set the port baud rate (for example, serialport.baurate = 115200). However, for me this did not work consistently, and I wondered if I had missed something.

Can someone illustrate the correct way to achieve this? Thank!